diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0fb9f394..042f902b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+### Version 4.1.0
+- Added $.isWindow
+- Made the TypeScript type system stricter
+- $.guid: ensuring it’s properly exported
+- $.fn.siblings: ensuring it supports multi-element collections
+- $.fn.empty: ensuring it supports multi-element collections
+- $.fn.attr: doing nothing when the value equals undefined
+
 ### Version 4.0.0
 - Removed `$.fn.removeData`
 - Removed `$.hasData`
diff --git a/README.md b/README.md
index 5784b67c..d1702b4a 100644
--- a/README.md
+++ b/README.md
@@ -30,10 +30,10 @@ If you're migrating from jQuery be sure to read our [migration guide](https://gi
 
 ## Usage
 
-Get Cash from [CloudFlare](https://cdnjs.cloudflare.com/ajax/libs/cash/4.0.0/cash.min.js) or [jsDelivr](https://cdn.jsdelivr.net/npm/cash-dom@4.0.0/dist/cash.min.js) and use it like this:
+Get Cash from [CloudFlare](https://cdnjs.cloudflare.com/ajax/libs/cash/4.1.0/cash.min.js) or [jsDelivr](https://cdn.jsdelivr.net/npm/cash-dom@4.1.0/dist/cash.min.js) and use it like this:
 
 ```html
-<script src="https://cdnjs.cloudflare.com/ajax/libs/cash/4.0.0/cash.min.js"></script>
+<script src="https://cdnjs.cloudflare.com/ajax/libs/cash/4.1.0/cash.min.js"></script>
 <script>
   $(function () {
     $('html').addClass ( 'dom-loaded' );
diff --git a/dist/cash.d.ts b/dist/cash.d.ts
index 6da1e2d2..e422b47c 100644
--- a/dist/cash.d.ts
+++ b/dist/cash.d.ts
@@ -1,8 +1,8 @@
 interface Cash {
-    [index: number]: Window & Document & HTMLElement & Element & Node;
+    [index: number]: Ele;
     length: number;
-    splice(start: number, deleteCount?: number): any;
-    splice(start: number, deleteCount: number, ...items: Ele[]): any;
+    splice(start: number, deleteCount?: number): Ele[];
+    splice(start: number, deleteCount: number, ...items: Ele[]): Ele[];
 }
 interface CashStatic {
     fn: Cash;
@@ -12,9 +12,18 @@ declare type plainObject = {
 };
 declare type falsy = undefined | null | false | 0 | '';
 declare type Ele = Window | Document | HTMLElement | Element | Node;
-declare type Selector = falsy | string | Function | HTMLCollection | NodeList | Ele | Ele[] | ArrayLike<any> | Cash;
-declare type Comparator = string | Function | Ele | Cash;
+declare type Selector = falsy | string | Function | HTMLCollection | NodeList | Ele | Ele[] | ArrayLike<Ele> | Cash;
+declare type Comparator = string | Ele | Cash | ((this: Ele, index: number, ele: Ele) => boolean);
 declare type Context = Document | HTMLElement | Element;
+declare type EventObj = Event & {
+    __delegate?: boolean;
+    namespace?: string;
+    data?: any;
+};
+declare type EventCallback = {
+    (event: EventObj, data?: any): any;
+    guid?: number;
+};
 declare class Cash {
     constructor(selector?: Selector, context?: Context | Cash);
     init(selector?: Selector, context?: Context | Cash): Cash;
@@ -33,8 +42,9 @@ interface Cash {
 interface Cash {
     last(): Cash;
 }
+declare type MapCallback<T> = (this: T, index: number, ele: T) => Ele;
 interface Cash {
-    map(callback: Function): Cash;
+    map(callback: MapCallback<Ele>): Cash;
 }
 interface Cash {
     slice(start?: number, end?: number): Cash;
@@ -42,11 +52,12 @@ interface Cash {
 interface CashStatic {
     camelCase(str: string): string;
 }
+declare type EachCallback<T> = (this: T, index: number, ele: T) => any;
 interface CashStatic {
-    each(arr: ArrayLike<any>, callback: Function): void;
+    each<T>(arr: ArrayLike<T>, callback: EachCallback<T>): void;
 }
 interface Cash {
-    each(callback: Function): this;
+    each(callback: EachCallback<Ele>): this;
 }
 interface Cash {
     removeProp(prop: string): this;
@@ -61,9 +72,10 @@ interface CashStatic {
     guid: number;
 }
 interface CashStatic {
-    matches(ele: HTMLElement, selector: string): boolean;
+    matches(ele: any, selector: string): boolean;
 }
 interface CashStatic {
+    isWindow(x: any): x is Window;
     isFunction(x: any): x is Function;
     isString(x: any): x is string;
     isNumeric(x: any): boolean;
@@ -84,8 +96,9 @@ interface Cash {
     removeAttr(attrs: string): this;
 }
 interface Cash {
-    attr(attrs: string): any;
-    attr(attrs: string, value: any): this;
+    attr(): undefined;
+    attr(attrs: string): string | null;
+    attr(attrs: string, value: string): this;
     attr(attrs: plainObject): this;
 }
 interface Cash {
@@ -98,7 +111,7 @@ interface Cash {
     removeClass(classes?: string): this;
 }
 interface CashStatic {
-    unique(arr: ArrayLike<any>): ArrayLike<any>;
+    unique<T>(arr: ArrayLike<T>): ArrayLike<T>;
 }
 interface Cash {
     add(selector: Selector, context?: Context): Cash;
@@ -107,8 +120,8 @@ interface CashStatic {
     prefixedProp(prop: string, isVariable?: boolean): string;
 }
 interface Cash {
-    css(prop: string): any;
-    css(prop: string, value: any): this;
+    css(prop: string): string | undefined;
+    css(prop: string, value: string): this;
     css(props: plainObject): this;
 }
 interface Cash {
@@ -118,8 +131,8 @@ interface Cash {
     data(datas: plainObject): this;
 }
 interface Cash {
-    innerWidth(): number;
-    innerHeight(): number;
+    innerWidth(): number | undefined;
+    innerHeight(): number | undefined;
 }
 interface Cash {
     width(): number;
@@ -143,31 +156,31 @@ interface Cash {
 interface Cash {
     off(): this;
     off(events: string): this;
-    off(events: string, callback: Function): this;
-    off(events: string, selector: string, callback: Function): this;
+    off(events: string, callback: EventCallback): this;
+    off(events: string, selector: string, callback: EventCallback): this;
 }
 interface Cash {
     on(events: plainObject): this;
-    on(events: string, callback: Function, _one?: boolean): this;
-    on(events: string, selector: string | Function, callback: Function, _one?: boolean): this;
+    on(events: string, callback: EventCallback, _one?: boolean): this;
+    on(events: string, selector: string | EventCallback, callback: EventCallback, _one?: boolean): this;
 }
 interface Cash {
     one(events: plainObject): this;
-    one(events: string, callback: Function): this;
-    one(events: string, selector: string | Function, callback: Function): this;
+    one(events: string, callback: EventCallback): this;
+    one(events: string, selector: string | EventCallback, callback: EventCallback): this;
 }
 interface Cash {
     ready(callback: Function): this;
 }
 interface Cash {
-    trigger(event: string | Event, data?: any): this;
+    trigger(event: Event | string, data?: any): this;
 }
 interface Cash {
     serialize(): string;
 }
 interface Cash {
     val(): string | string[];
-    val(value: any): this;
+    val(value: string | string[]): this;
 }
 interface Cash {
     clone(): this;
diff --git a/dist/cash.esm.js b/dist/cash.esm.js
index 96bc9c6f..a62470ff 100644
--- a/dist/cash.esm.js
+++ b/dist/cash.esm.js
@@ -3,7 +3,7 @@ const doc = document, win = window, div = doc.createElement('div'), { filter, in
 const idRe = /^#[\w-]*$/, classRe = /^\.[\w-]*$/, htmlRe = /<.+>/, tagRe = /^\w+$/;
 // @require ./variables.ts
 function find(selector, context = doc) {
-    return context !== doc && context.nodeType !== 1 && context.nodeType !== 9
+    return !isDocument(context) && !isElement(context)
         ? []
         : classRe.test(selector)
             ? context.getElementsByClassName(selector.slice(1))
@@ -47,7 +47,7 @@ class Cash {
 const cash = Cash.prototype.init;
 cash.fn = cash.prototype = Cash.prototype; // Ensuring that `cash () instanceof cash`
 Cash.prototype.length = 0;
-Cash.prototype.splice = splice; // Ensuring a cash collection gets printed as array-like in Chrome
+Cash.prototype.splice = splice; // Ensuring a cash collection gets printed as array-like in Chrome's devtools
 if (typeof Symbol === 'function') {
     Cash.prototype[Symbol['iterator']] = Array.prototype[Symbol['iterator']];
 }
@@ -73,14 +73,13 @@ Cash.prototype.slice = function () {
 };
 // @require ./cash.ts
 const dashAlphaRe = /-([a-z])/g;
-function camelCaseReplace(all, letter) {
+function camelCaseReplace(match, letter) {
     return letter.toUpperCase();
 }
 function camelCase(str) {
     return str.replace(dashAlphaRe, camelCaseReplace);
 }
 cash.camelCase = camelCase;
-// @require ./cash.ts
 function each(arr, callback) {
     for (let i = 0, l = arr.length; i < l; i++) {
         if (callback.call(arr[i], i, arr[i]) === false)
@@ -97,9 +96,9 @@ Cash.prototype.removeProp = function (prop) {
 };
 // @require ./cash.ts
 function extend(target, ...objs) {
-    let args = arguments, length = args.length;
+    const args = arguments, length = args.length;
     for (let i = (length < 2 ? 0 : 1); i < length; i++) {
-        for (let key in args[i]) {
+        for (const key in args[i]) {
             target[key] = args[i][key];
         }
     }
@@ -109,12 +108,10 @@ Cash.prototype.extend = function (plugins) {
     return extend(cash.fn, plugins);
 };
 cash.extend = extend;
-// @require ./cash.ts
-let guid = 1;
-cash.guid = guid;
+cash.guid = 1;
 // @require ./cash.ts
 function matches(ele, selector) {
-    const matches = ele && (ele.matches || ele['webkitMatchesSelector'] || ele['mozMatchesSelector'] || ele['msMatchesSelector'] || ele['oMatchesSelector']);
+    const matches = ele && (ele['matches'] || ele['webkitMatchesSelector'] || ele['mozMatchesSelector'] || ele['msMatchesSelector'] || ele['oMatchesSelector']);
     return !!matches && matches.call(ele, selector);
 }
 cash.matches = matches;
@@ -136,6 +133,15 @@ function pluck(arr, prop, deep) {
 function isCash(x) {
     return x instanceof Cash;
 }
+function isWindow(x) {
+    return !!x && x === x.window;
+}
+function isDocument(x) {
+    return !!x && x.nodeType === 9;
+}
+function isElement(x) {
+    return !!x && x.nodeType === 1;
+}
 function isFunction(x) {
     return typeof x === 'function';
 }
@@ -146,6 +152,7 @@ function isNumeric(x) {
     return !isNaN(parseFloat(x)) && isFinite(x);
 }
 const { isArray } = Array;
+cash.isWindow = isWindow;
 cash.isFunction = isFunction;
 cash.isString = isString;
 cash.isNumeric = isNumeric;
@@ -158,7 +165,7 @@ Cash.prototype.prop = function (prop, value) {
             return this[0] && this[0][prop];
         return this.each((i, ele) => { ele[prop] = value; });
     }
-    for (let key in prop) {
+    for (const key in prop) {
         this.prop(key, prop[key]);
     }
     return this;
@@ -190,7 +197,7 @@ function getSplitValues(str) {
     return isString(str) ? str.match(splitValuesRe) || [] : [];
 }
 Cash.prototype.hasClass = function (cls) {
-    return cls && some.call(this, ele => ele.classList.contains(cls));
+    return cls && some.call(this, (ele) => ele.classList.contains(cls));
 };
 Cash.prototype.removeAttr = function (attr) {
     const attrs = getSplitValues(attr);
@@ -212,11 +219,13 @@ function attr(attr, value) {
             const value = this[0].getAttribute(attr);
             return value === null ? undefined : value;
         }
+        if (value === undefined)
+            return this;
         if (value === null)
             return this.removeAttr(attr);
         return this.each((i, ele) => { ele.setAttribute(attr, value); });
     }
-    for (let key in attr) {
+    for (const key in attr) {
         this.attr(key, attr[key]);
     }
     return this;
@@ -260,9 +269,10 @@ cash.unique = unique;
 Cash.prototype.add = function (selector, context) {
     return cash(unique(this.get().concat(cash(selector, context).get())));
 };
+// @require core/type_checking.ts
 // @require core/variables.ts
 function computeStyle(ele, prop, isVariable) {
-    if (ele.nodeType !== 1 || !prop)
+    if (!isElement(ele) || !prop)
         return;
     const style = win.getComputedStyle(ele, null);
     return prop ? (isVariable ? style.getPropertyValue(prop) || undefined : style[prop]) : style;
@@ -326,17 +336,17 @@ function css(prop, value) {
             return this;
         value = getSuffixedValue(prop, value, isVariable);
         return this.each((i, ele) => {
-            if (ele.nodeType !== 1)
+            if (!isElement(ele))
                 return;
             if (isVariable) {
-                ele.style.setProperty(prop, value);
+                ele.style.setProperty(prop, value); //TSC
             }
             else {
                 ele.style[prop] = value; //TSC
             }
         });
     }
-    for (let key in prop) {
+    for (const key in prop) {
         this.css(key, prop[key]);
     }
     return this;
@@ -385,7 +395,7 @@ function data(name, value) {
             return this[0] && getData(this[0], name);
         return this.each((i, ele) => setData(ele, name, value));
     }
-    for (let key in name) {
+    for (const key in name) {
         this.data(key, name[key]);
     }
     return this;
@@ -400,7 +410,7 @@ each(['Width', 'Height'], (i, prop) => {
     Cash.prototype[`inner${prop}`] = function () {
         if (!this[0])
             return;
-        if (this[0] === win)
+        if (isWindow(this[0]))
             return win[`inner${prop}`];
         return this[0][`client${prop}`];
     };
@@ -410,13 +420,13 @@ each(['width', 'height'], (index, prop) => {
         if (!this[0])
             return value === undefined ? undefined : this;
         if (!arguments.length) {
-            if (this[0] === win)
+            if (isWindow(this[0]))
                 return this[0][camelCase(`outer-${prop}`)];
             return this[0].getBoundingClientRect()[prop] - getExtraSpace(this[0], !index);
         }
-        const valueNumber = parseInt(value, 10);
+        const valueNumber = parseInt(value, 10); //TSC
         return this.each((i, ele) => {
-            if (ele.nodeType !== 1)
+            if (!isElement(ele))
                 return;
             const boxSizing = computeStyle(ele, 'boxSizing');
             ele.style[prop] = getSuffixedValue(prop, valueNumber + (boxSizing === 'border-box' ? getExtraSpace(ele, !index) : 0));
@@ -427,7 +437,7 @@ each(['Width', 'Height'], (index, prop) => {
     Cash.prototype[`outer${prop}`] = function (includeMargins) {
         if (!this[0])
             return;
-        if (this[0] === win)
+        if (isWindow(this[0]))
             return win[`outer${prop}`];
         return this[0][`offset${prop}`] + (includeMargins ? computeStyleInt(this[0], `margin${!index ? 'Left' : 'Top'}`) + computeStyleInt(this[0], `margin${!index ? 'Right' : 'Bottom'}`) : 0);
     };
@@ -474,7 +484,7 @@ Cash.prototype.show = function () {
 // @optional ./show.ts
 // @optional ./toggle.ts
 function hasNamespaces(ns1, ns2) {
-    return !ns2 || !some.call(ns2, ns => ns1.indexOf(ns) < 0);
+    return !ns2 || !some.call(ns2, (ns) => ns1.indexOf(ns) < 0);
 }
 const eventsNamespace = '__cashEvents', eventsNamespacesSeparator = '.', eventsFocus = { focus: 'focusin', blur: 'focusout' }, eventsHover = { mouseenter: 'mouseover', mouseleave: 'mouseout' }, eventsMouseRe = /^(?:mouse|pointer|contextmenu|drag|drop|click|dblclick)/i;
 // @require ./variables.ts
@@ -488,11 +498,11 @@ function getEventsCache(ele) {
 // @require core/guid.ts
 // @require events/helpers/get_events_cache.ts
 function addEvent(ele, name, namespaces, selector, callback) {
-    callback['guid'] = (callback['guid'] || guid++);
+    callback.guid = callback.guid || cash.guid++;
     const eventCache = getEventsCache(ele);
     eventCache[name] = (eventCache[name] || []);
     eventCache[name].push([namespaces, selector, callback]);
-    ele.addEventListener(name, callback); //TSC
+    ele.addEventListener(name, callback);
 }
 // @require ./variables.ts
 function parseEventName(eventName) {
@@ -512,7 +522,7 @@ function removeEvent(ele, name, namespaces, selector, callback) {
     }
     else if (cache[name]) {
         cache[name] = cache[name].filter(([ns, sel, cb]) => {
-            if ((callback && cb['guid'] !== callback['guid']) || !hasNamespaces(ns, namespaces) || (selector && selector !== sel))
+            if ((callback && cb.guid !== callback.guid) || !hasNamespaces(ns, namespaces) || (selector && selector !== sel))
                 return true;
             ele.removeEventListener(name, cb);
         });
@@ -536,7 +546,7 @@ Cash.prototype.off = function (eventFullName, selector, callback) {
 };
 function on(eventFullName, selector, callback, _one) {
     if (!isString(eventFullName)) {
-        for (let key in eventFullName) {
+        for (const key in eventFullName) {
             this.on(key, selector, eventFullName[key]);
         }
         return this;
@@ -557,7 +567,7 @@ function on(eventFullName, selector, callback, _one) {
                     while (!matches(target, selector)) { //TSC
                         if (target === ele)
                             return;
-                        target = target.parentNode;
+                        target = target['parentNode'];
                         if (!target)
                             return;
                     }
@@ -581,7 +591,7 @@ function on(eventFullName, selector, callback, _one) {
                     event.stopPropagation();
                 }
             };
-            finalCallback['guid'] = callback['guid'] = (callback['guid'] || guid++);
+            finalCallback.guid = callback['guid'] = (callback['guid'] || cash.guid++); //TSC
             addEvent(ele, name, namespaces, selector, finalCallback); //TSC
         });
     });
@@ -604,18 +614,21 @@ Cash.prototype.ready = function (callback) {
     return this;
 };
 Cash.prototype.trigger = function (eventFullName, data) {
-    let evt = eventFullName;
+    let evt;
     if (isString(eventFullName)) {
         const [name, namespaces] = parseEventName(eventFullName), type = eventsMouseRe.test(name) ? 'MouseEvents' : 'HTMLEvents';
         evt = doc.createEvent(type);
         evt.initEvent(name, true, true);
-        evt['namespace'] = namespaces.join(eventsNamespacesSeparator);
+        evt.namespace = namespaces.join(eventsNamespacesSeparator);
+    }
+    else {
+        evt = eventFullName;
     }
-    evt['data'] = data;
-    const isEventFocus = (evt['type'] in eventsFocus);
+    evt.data = data;
+    const isEventFocus = (evt.type in eventsFocus);
     return this.each((i, ele) => {
-        if (isEventFocus && isFunction(ele[evt['type']])) {
-            ele[evt['type']]();
+        if (isEventFocus && isFunction(ele[evt.type])) {
+            ele[evt.type]();
         }
         else {
             ele.dispatchEvent(evt);
@@ -720,13 +733,11 @@ function parseHTML(html) {
 }
 cash.parseHTML = parseHTML;
 Cash.prototype.empty = function () {
-    const ele = this[0];
-    if (ele) {
+    return this.each((i, ele) => {
         while (ele.firstChild) {
             ele.removeChild(ele.firstChild);
         }
-    }
-    return this;
+    });
 };
 function html(html) {
     if (html === undefined)
@@ -777,12 +788,14 @@ Cash.prototype.position = function () {
     };
 };
 Cash.prototype.children = function (comparator) {
-    let result = [];
-    this.each((i, ele) => { push.apply(result, ele.children); });
+    const result = [];
+    this.each((i, ele) => {
+        push.apply(result, ele.children);
+    });
     return filtered(cash(unique(result)), comparator);
 };
 Cash.prototype.contents = function () {
-    let result = [];
+    const result = [];
     this.each((i, ele) => {
         push.apply(result, ele.tagName === 'IFRAME' ? [ele.contentDocument] : ele.childNodes);
     });
@@ -799,7 +812,6 @@ Cash.prototype.find = function (selector) {
     return cash(unique(result));
 };
 // @require collection/filter.ts
-// @require collection/filter.ts
 // @require traversal/find.ts
 const scriptTypeRe = /^$|^module$|\/(?:java|ecma)script/i, HTMLCDATARe = /^\s*<!(?:\[CDATA\[|--)|(?:\]\]|--)>\s*$/g;
 function evalScripts(node) {
@@ -970,8 +982,11 @@ Cash.prototype.prevAll = function (comparator) {
     return this.prev(comparator, true);
 };
 Cash.prototype.siblings = function (comparator) {
-    const ele = this[0];
-    return filtered(this.parent().children().filter((i, child) => child !== ele), comparator);
+    const result = [];
+    this.each((i, ele) => {
+        push.apply(result, cash(ele).parent().children((ci, child) => child !== ele));
+    });
+    return filtered(cash(unique(result)), comparator);
 };
 // @optional ./children.ts
 // @optional ./closest.ts
diff --git a/dist/cash.js b/dist/cash.js
index 26c58cb2..c2f023ed 100644
--- a/dist/cash.js
+++ b/dist/cash.js
@@ -24,7 +24,7 @@ function find(selector, context) {
     context = doc;
   }
 
-  return context !== doc && context.nodeType !== 1 && context.nodeType !== 9 ? [] : classRe.test(selector) ? context.getElementsByClassName(selector.slice(1)) : tagRe.test(selector) ? context.getElementsByTagName(selector) : context.querySelectorAll(selector);
+  return !isDocument(context) && !isElement(context) ? [] : classRe.test(selector) ? context.getElementsByClassName(selector.slice(1)) : tagRe.test(selector) ? context.getElementsByTagName(selector) : context.querySelectorAll(selector);
 } // @require ./find.ts
 // @require ./variables.ts
 
@@ -68,7 +68,7 @@ var cash = Cash.prototype.init;
 cash.fn = cash.prototype = Cash.prototype; // Ensuring that `cash () instanceof cash`
 
 Cash.prototype.length = 0;
-Cash.prototype.splice = splice; // Ensuring a cash collection gets printed as array-like in Chrome
+Cash.prototype.splice = splice; // Ensuring a cash collection gets printed as array-like in Chrome's devtools
 
 if (typeof Symbol === 'function') {
   Cash.prototype[Symbol['iterator']] = Array.prototype[Symbol['iterator']];
@@ -104,7 +104,7 @@ Cash.prototype.slice = function () {
 
 var dashAlphaRe = /-([a-z])/g;
 
-function camelCaseReplace(all, letter) {
+function camelCaseReplace(match, letter) {
   return letter.toUpperCase();
 }
 
@@ -112,7 +112,7 @@ function camelCase(str) {
   return str.replace(dashAlphaRe, camelCaseReplace);
 }
 
-cash.camelCase = camelCase; // @require ./cash.ts
+cash.camelCase = camelCase;
 
 function each(arr, callback) {
   for (var i = 0, l = arr.length; i < l; i++) {
@@ -157,13 +157,11 @@ Cash.prototype.extend = function (plugins) {
   return extend(cash.fn, plugins);
 };
 
-cash.extend = extend; // @require ./cash.ts
-
-var guid = 1;
-cash.guid = guid; // @require ./cash.ts
+cash.extend = extend;
+cash.guid = 1; // @require ./cash.ts
 
 function matches(ele, selector) {
-  var matches = ele && (ele.matches || ele['webkitMatchesSelector'] || ele['mozMatchesSelector'] || ele['msMatchesSelector'] || ele['oMatchesSelector']);
+  var matches = ele && (ele['matches'] || ele['webkitMatchesSelector'] || ele['mozMatchesSelector'] || ele['msMatchesSelector'] || ele['oMatchesSelector']);
   return !!matches && matches.call(ele, selector);
 }
 
@@ -190,6 +188,18 @@ function isCash(x) {
   return x instanceof Cash;
 }
 
+function isWindow(x) {
+  return !!x && x === x.window;
+}
+
+function isDocument(x) {
+  return !!x && x.nodeType === 9;
+}
+
+function isElement(x) {
+  return !!x && x.nodeType === 1;
+}
+
 function isFunction(x) {
   return typeof x === 'function';
 }
@@ -203,6 +213,7 @@ function isNumeric(x) {
 }
 
 var isArray = Array.isArray;
+cash.isWindow = isWindow;
 cash.isFunction = isFunction;
 cash.isString = isString;
 cash.isNumeric = isNumeric;
@@ -283,6 +294,7 @@ function attr(attr, value) {
       return value_1 === null ? undefined : value_1;
     }
 
+    if (value === undefined) return this;
     if (value === null) return this.removeAttr(attr);
     return this.each(function (i, ele) {
       ele.setAttribute(attr, value);
@@ -341,11 +353,12 @@ cash.unique = unique;
 
 Cash.prototype.add = function (selector, context) {
   return cash(unique(this.get().concat(cash(selector, context).get())));
-}; // @require core/variables.ts
+}; // @require core/type_checking.ts
+// @require core/variables.ts
 
 
 function computeStyle(ele, prop, isVariable) {
-  if (ele.nodeType !== 1 || !prop) return;
+  if (!isElement(ele) || !prop) return;
   var style = win.getComputedStyle(ele, null);
   return prop ? isVariable ? style.getPropertyValue(prop) || undefined : style[prop] : style;
 } // @require ./compute_style.ts
@@ -426,10 +439,10 @@ function css(prop, value) {
     if (!prop) return this;
     value = getSuffixedValue(prop, value, isVariable_1);
     return this.each(function (i, ele) {
-      if (ele.nodeType !== 1) return;
+      if (!isElement(ele)) return;
 
       if (isVariable_1) {
-        ele.style.setProperty(prop, value);
+        ele.style.setProperty(prop, value); //TSC
       } else {
         ele.style[prop] = value; //TSC
       }
@@ -510,7 +523,7 @@ function getExtraSpace(ele, xAxis) {
 each(['Width', 'Height'], function (i, prop) {
   Cash.prototype["inner" + prop] = function () {
     if (!this[0]) return;
-    if (this[0] === win) return win["inner" + prop];
+    if (isWindow(this[0])) return win["inner" + prop];
     return this[0]["client" + prop];
   };
 });
@@ -519,13 +532,14 @@ each(['width', 'height'], function (index, prop) {
     if (!this[0]) return value === undefined ? undefined : this;
 
     if (!arguments.length) {
-      if (this[0] === win) return this[0][camelCase("outer-" + prop)];
+      if (isWindow(this[0])) return this[0][camelCase("outer-" + prop)];
       return this[0].getBoundingClientRect()[prop] - getExtraSpace(this[0], !index);
     }
 
-    var valueNumber = parseInt(value, 10);
+    var valueNumber = parseInt(value, 10); //TSC
+
     return this.each(function (i, ele) {
-      if (ele.nodeType !== 1) return;
+      if (!isElement(ele)) return;
       var boxSizing = computeStyle(ele, 'boxSizing');
       ele.style[prop] = getSuffixedValue(prop, valueNumber + (boxSizing === 'border-box' ? getExtraSpace(ele, !index) : 0));
     });
@@ -534,7 +548,7 @@ each(['width', 'height'], function (index, prop) {
 each(['Width', 'Height'], function (index, prop) {
   Cash.prototype["outer" + prop] = function (includeMargins) {
     if (!this[0]) return;
-    if (this[0] === win) return win["outer" + prop];
+    if (isWindow(this[0])) return win["outer" + prop];
     return this[0]["offset" + prop] + (includeMargins ? computeStyleInt(this[0], "margin" + (!index ? 'Left' : 'Top')) + computeStyleInt(this[0], "margin" + (!index ? 'Right' : 'Bottom')) : 0);
   };
 }); // @optional ./inner.ts
@@ -615,11 +629,11 @@ function getEventsCache(ele) {
 
 
 function addEvent(ele, name, namespaces, selector, callback) {
-  callback['guid'] = callback['guid'] || guid++;
+  callback.guid = callback.guid || cash.guid++;
   var eventCache = getEventsCache(ele);
   eventCache[name] = eventCache[name] || [];
   eventCache[name].push([namespaces, selector, callback]);
-  ele.addEventListener(name, callback); //TSC
+  ele.addEventListener(name, callback);
 } // @require ./variables.ts
 
 
@@ -645,7 +659,7 @@ function removeEvent(ele, name, namespaces, selector, callback) {
       var ns = _a[0],
           sel = _a[1],
           cb = _a[2];
-      if (callback && cb['guid'] !== callback['guid'] || !hasNamespaces(ns, namespaces) || selector && selector !== sel) return true;
+      if (callback && cb.guid !== callback.guid || !hasNamespaces(ns, namespaces) || selector && selector !== sel) return true;
       ele.removeEventListener(name, cb);
     });
   }
@@ -711,7 +725,7 @@ function on(eventFullName, selector, callback, _one) {
           while (!matches(target, selector)) {
             //TSC
             if (target === ele) return;
-            target = target.parentNode;
+            target = target['parentNode'];
             if (!target) return;
           }
 
@@ -740,7 +754,8 @@ function on(eventFullName, selector, callback, _one) {
         }
       };
 
-      finalCallback['guid'] = callback['guid'] = callback['guid'] || guid++;
+      finalCallback.guid = callback['guid'] = callback['guid'] || cash.guid++; //TSC
+
       addEvent(ele, name, namespaces, selector, finalCallback); //TSC
     });
   });
@@ -771,7 +786,7 @@ Cash.prototype.ready = function (callback) {
 };
 
 Cash.prototype.trigger = function (eventFullName, data) {
-  var evt = eventFullName;
+  var evt;
 
   if (isString(eventFullName)) {
     var _a = parseEventName(eventFullName),
@@ -781,14 +796,16 @@ Cash.prototype.trigger = function (eventFullName, data) {
 
     evt = doc.createEvent(type);
     evt.initEvent(name_1, true, true);
-    evt['namespace'] = namespaces.join(eventsNamespacesSeparator);
+    evt.namespace = namespaces.join(eventsNamespacesSeparator);
+  } else {
+    evt = eventFullName;
   }
 
-  evt['data'] = data;
-  var isEventFocus = evt['type'] in eventsFocus;
+  evt.data = data;
+  var isEventFocus = evt.type in eventsFocus;
   return this.each(function (i, ele) {
-    if (isEventFocus && isFunction(ele[evt['type']])) {
-      ele[evt['type']]();
+    if (isEventFocus && isFunction(ele[evt.type])) {
+      ele[evt.type]();
     } else {
       ele.dispatchEvent(evt);
     }
@@ -906,15 +923,11 @@ function parseHTML(html) {
 cash.parseHTML = parseHTML;
 
 Cash.prototype.empty = function () {
-  var ele = this[0];
-
-  if (ele) {
+  return this.each(function (i, ele) {
     while (ele.firstChild) {
       ele.removeChild(ele.firstChild);
     }
-  }
-
-  return this;
+  });
 };
 
 function html(html) {
@@ -1004,7 +1017,6 @@ Cash.prototype.find = function (selector) {
 
   return cash(unique(result));
 }; // @require collection/filter.ts
-// @require collection/filter.ts
 // @require traversal/find.ts
 
 
@@ -1228,10 +1240,13 @@ Cash.prototype.prevAll = function (comparator) {
 };
 
 Cash.prototype.siblings = function (comparator) {
-  var ele = this[0];
-  return filtered(this.parent().children().filter(function (i, child) {
-    return child !== ele;
-  }), comparator);
+  var result = [];
+  this.each(function (i, ele) {
+    push.apply(result, cash(ele).parent().children(function (ci, child) {
+      return child !== ele;
+    }));
+  });
+  return filtered(cash(unique(result)), comparator);
 }; // @optional ./children.ts
 // @optional ./closest.ts
 // @optional ./contents.ts
diff --git a/dist/cash.min.js b/dist/cash.min.js
index 99a784f3..39e635b9 100644
--- a/dist/cash.min.js
+++ b/dist/cash.min.js
@@ -1,37 +1,37 @@
 /* MIT https://github.com/kenwheeler/cash */
 (function(){
-'use strict';var e=document,f=window,k=e.createElement("div"),l=Array.prototype,m=l.filter,n=l.indexOf,aa=l.map,q=l.push,r=l.reverse,u=l.slice,v=l.some,ba=l.splice,ca=/^#[\w-]*$/,da=/^\.[\w-]*$/,ea=/<.+>/,fa=/^\w+$/;function x(a,b){void 0===b&&(b=e);return b!==e&&1!==b.nodeType&&9!==b.nodeType?[]:da.test(a)?b.getElementsByClassName(a.slice(1)):fa.test(a)?b.getElementsByTagName(a):b.querySelectorAll(a)}
-var y=function(){function a(a,c){void 0===c&&(c=e);if(a){if(a instanceof y)return a;var b=a;if(z(a)){if(b=c instanceof y?c[0]:c,b=ca.test(a)?b.getElementById(a.slice(1)):ea.test(a)?A(a):x(a,b),!b)return}else if(B(a))return this.ready(a);if(b.nodeType||b===f)b=[b];this.length=b.length;a=0;for(c=this.length;a<c;a++)this[a]=b[a]}}a.prototype.init=function(b,c){return new a(b,c)};return a}(),C=y.prototype.init;C.fn=C.prototype=y.prototype;y.prototype.length=0;y.prototype.splice=ba;
+'use strict';var e=document,g=window,k=e.createElement("div"),l=Array.prototype,m=l.filter,n=l.indexOf,aa=l.map,q=l.push,r=l.reverse,u=l.slice,v=l.some,ba=l.splice,ca=/^#[\w-]*$/,da=/^\.[\w-]*$/,ea=/<.+>/,fa=/^\w+$/;function x(a,b){void 0===b&&(b=e);return b&&9===b.nodeType||b&&1===b.nodeType?da.test(a)?b.getElementsByClassName(a.slice(1)):fa.test(a)?b.getElementsByTagName(a):b.querySelectorAll(a):[]}
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+y.prototype.toggle=function(a){return this.each(function(b,c){if(a=void 0!==a?a:"none"===P(c,"display")){if(c.style.display="","none"===P(c,"display")){b=c.style;c=c.tagName;if(T[c])c=T[c];else{var d=e.createElement(c);e.body.appendChild(d);var f=P(d,"display");e.body.removeChild(d);c=T[c]="none"!==f?f:"block"}b.display=c}}else c.style.display="none"})};y.prototype.hide=function(){return this.toggle(!1)};y.prototype.show=function(){return this.toggle(!0)};
+function sa(a,b){return!b||!v.call(b,function(b){return 0>a.indexOf(b)})}var U={focus:"focusin",blur:"focusout"},ta={mouseenter:"mouseover",mouseleave:"mouseout"},ua=/^(?:mouse|pointer|contextmenu|drag|drop|click|dblclick)/i;function va(a,b,c,d,f){f.guid=f.guid||C.guid++;var h=a.__cashEvents=a.__cashEvents||{};h[b]=h[b]||[];h[b].push([c,d,f]);a.addEventListener(b,f)}function V(a){a=a.split(".");return[a[0],a.slice(1).sort()]}
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+!1===t&&(a.preventDefault(),a.stopPropagation())}};a.guid=c.guid=c.guid||C.guid++;va(h,p,w,b,a)})});return this};y.prototype.one=function(a,b,c){return this.on(a,b,c,!0)};y.prototype.ready=function(a){function b(){return a(C)}"loading"!==e.readyState?setTimeout(b):e.addEventListener("DOMContentLoaded",b);return this};
+y.prototype.trigger=function(a,b){if(z(a)){var c=V(a);a=c[0];c=c[1];var d=ua.test(a)?"MouseEvents":"HTMLEvents";var f=e.createEvent(d);f.initEvent(a,!0,!0);f.namespace=c.join(".")}else f=a;f.data=b;var h=f.type in U;return this.each(function(a,b){if(h&&B(b[f.type]))b[f.type]();else b.dispatchEvent(f)})};function wa(a){return a.multiple?H(m.call(a.options,function(a){return a.selected&&!a.disabled&&!a.parentNode.disabled}),"value"):a.value||""}
+var xa=/%20/g,Aa=/file|reset|submit|button|image/i,Ba=/radio|checkbox/i;y.prototype.serialize=function(){var a="";this.each(function(b,c){E(c.elements||[c],function(b,c){c.disabled||!c.name||"FIELDSET"===c.tagName||Aa.test(c.type)||Ba.test(c.type)&&!c.checked||(b=wa(c),void 0!==b&&(b=K(b)?b:[b],E(b,function(b,d){b=a;d="&"+encodeURIComponent(c.name)+"="+encodeURIComponent(d).replace(xa,"+");a=b+d})))})});return a.substr(1)};
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+function A(a){if(!X){var b=e.createElement("table"),c=e.createElement("tr");X={"*":k,tr:e.createElement("tbody"),td:c,th:c,thead:b,tbody:b,tfoot:b}}if(!z(a))return[];if(Da.test(a))return[e.createElement(RegExp.$1)];b=Ca.test(a)&&RegExp.$1;b=X[b]||X["*"];b.innerHTML=a;return C(b.childNodes).detach().get()}C.parseHTML=A;y.prototype.empty=function(){return this.each(function(a,b){for(;b.firstChild;)b.removeChild(b.firstChild)})};
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+y.prototype.offset=function(){var a=this[0];if(a)return a=a.getBoundingClientRect(),{top:a.top+g.pageYOffset-Ea.clientTop,left:a.left+g.pageXOffset-Ea.clientLeft}};y.prototype.offsetParent=function(){return C(this[0]&&this[0].offsetParent)};y.prototype.position=function(){var a=this[0];if(a)return{left:a.offsetLeft,top:a.offsetTop}};y.prototype.children=function(a){var b=[];this.each(function(a,d){q.apply(b,d.children)});return M(C(O(b)),a)};
+y.prototype.contents=function(){var a=[];this.each(function(b,c){q.apply(a,"IFRAME"===c.tagName?[c.contentDocument]:c.childNodes)});return C(O(a))};y.prototype.find=function(a){for(var b=[],c=0,d=this.length;c<d;c++){var f=x(a,this[c]);f.length&&q.apply(b,f)}return C(O(b))};var Fa=/^$|^module$|\/(?:java|ecma)script/i,Ga=/^\s*<!(?:\[CDATA\[|--)|(?:\]\]|--)>\s*$/g;
+function Y(a){a=C(a);a.filter("script").add(a.find("script")).each(function(a,c){!c.src&&Fa.test(c.type)&&c.ownerDocument.documentElement.contains(c)&&eval(c.textContent.replace(Ga,""))})}function Z(a,b,c){E(a,function(a,f){E(b,function(b,d){b=a?d.cloneNode(!0):d;c?f.insertBefore(b,c&&f.firstChild):f.appendChild(b);Y(b)})})}y.prototype.append=function(){var a=this;E(arguments,function(b,c){Z(a,C(c))});return this};y.prototype.appendTo=function(a){Z(C(a),this);return this};
+y.prototype.insertAfter=function(a){var b=this;C(a).each(function(a,d){var c=d.parentNode;c&&b.each(function(b,f){b=a?f.cloneNode(!0):f;c.insertBefore(b,d.nextSibling);Y(b)})});return this};y.prototype.after=function(){var a=this;E(r.apply(arguments),function(b,c){r.apply(C(c).slice()).insertAfter(a)});return this};y.prototype.insertBefore=function(a){var b=this;C(a).each(function(a,d){var c=d.parentNode;c&&b.each(function(b,f){b=a?f.cloneNode(!0):f;c.insertBefore(b,d);Y(b)})});return this};
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-y.prototype.has=function(a){var b=z(a)?function(b,d){return!!x(a,d).length}:function(b,d){return d.contains(a)};return this.filter(b)};y.prototype.is=function(a){if(!a||!this[0])return!1;var b=L(a),c=!1;this.each(function(a,g){c=b.call(g,a,g);return!c});return c};y.prototype.next=function(a,b){return M(C(O(I(this,"nextElementSibling",b))),a)};y.prototype.nextAll=function(a){return this.next(a,!0)};
-y.prototype.not=function(a){if(!a||!this[0])return this;var b=L(a);return this.filter(function(a,d){return!b.call(d,a,d)})};y.prototype.parent=function(a){return M(C(O(I(this,"parentNode"))),a)};y.prototype.index=function(a){var b=a?C(a)[0]:this[0];a=a?this:C(b).parent().children();return n.call(a,b)};y.prototype.closest=function(a){if(!a||!this[0])return C();var b=this.filter(a);return b.length?b:this.parent().closest(a)};
-y.prototype.parents=function(a){return M(C(O(I(this,"parentElement",!0))),a)};y.prototype.prev=function(a,b){return M(C(O(I(this,"previousElementSibling",b))),a)};y.prototype.prevAll=function(a){return this.prev(a,!0)};y.prototype.siblings=function(a){var b=this[0];return M(this.parent().children().filter(function(a,d){return d!==b}),a)};"undefined"!==typeof exports?module.exports=C:f.cash=f.$=C;
+y.prototype.has=function(a){var b=z(a)?function(b,d){return!!x(a,d).length}:function(b,d){return d.contains(a)};return this.filter(b)};y.prototype.is=function(a){if(!a||!this[0])return!1;var b=L(a),c=!1;this.each(function(a,f){c=b.call(f,a,f);return!c});return c};y.prototype.next=function(a,b){return M(C(O(H(this,"nextElementSibling",b))),a)};y.prototype.nextAll=function(a){return this.next(a,!0)};
+y.prototype.not=function(a){if(!a||!this[0])return this;var b=L(a);return this.filter(function(a,d){return!b.call(d,a,d)})};y.prototype.parent=function(a){return M(C(O(H(this,"parentNode"))),a)};y.prototype.index=function(a){var b=a?C(a)[0]:this[0];a=a?this:C(b).parent().children();return n.call(a,b)};y.prototype.closest=function(a){if(!a||!this[0])return C();var b=this.filter(a);return b.length?b:this.parent().closest(a)};
+y.prototype.parents=function(a){return M(C(O(H(this,"parentElement",!0))),a)};y.prototype.prev=function(a,b){return M(C(O(H(this,"previousElementSibling",b))),a)};y.prototype.prevAll=function(a){return this.prev(a,!0)};y.prototype.siblings=function(a){var b=[];this.each(function(a,d){q.apply(b,C(d).parent().children(function(a,b){return b!==d}))});return M(C(O(b)),a)};"undefined"!==typeof exports?module.exports=C:g.cash=g.$=C;
 })();
\ No newline at end of file
diff --git a/dist/cash.ts b/dist/cash.ts
index 78bf3cab..7ddbd320 100644
--- a/dist/cash.ts
+++ b/dist/cash.ts
@@ -1,9 +1,9 @@
 
 interface Cash {
-  [index: number]: Window & Document & HTMLElement & Element & Node; //FIXME: Quick and dirty way of getting rid of most type errors
+  [index: number]: Ele;
   length: number;
-  splice ( start: number, deleteCount?: number );
-  splice ( start: number, deleteCount: number, ...items: Ele[] );
+  splice ( start: number, deleteCount?: number ): Ele[];
+  splice ( start: number, deleteCount: number, ...items: Ele[] ): Ele[];
 }
 
 interface CashStatic {
@@ -14,10 +14,21 @@ type plainObject = { [index: string]: any };
 type falsy = undefined | null | false | 0 | '';
 
 type Ele = Window | Document | HTMLElement | Element | Node;
-type Selector = falsy | string | Function | HTMLCollection | NodeList | Ele | Ele[] | ArrayLike<any> | Cash;
-type Comparator = string | Function | Ele | Cash;
+type Selector = falsy | string | Function | HTMLCollection | NodeList | Ele | Ele[] | ArrayLike<Ele> | Cash;
+type Comparator = string | Ele | Cash | (( this: Ele, index: number, ele: Ele ) => boolean);
 type Context = Document | HTMLElement | Element;
 
+type EventObj = Event & {
+  __delegate?: boolean,
+  namespace?: string,
+  data?: any
+};
+
+type EventCallback = {
+  ( event: EventObj, data?: any ): any,
+  guid?: number
+};
+
 
 const doc = document,
       win = window,
@@ -32,9 +43,9 @@ const idRe = /^#[\w-]*$/,
 
 // @require ./variables.ts
 
-function find ( selector: string, context: Context = doc ) {
+function find ( selector: string, context: Ele = doc ): ArrayLike<Element> {
 
-  return context !== doc && context.nodeType !== 1 && context.nodeType !== 9
+  return !isDocument ( context ) && !isElement ( context )
            ? []
            : classRe.test ( selector )
              ? context.getElementsByClassName ( selector.slice ( 1 ) )
@@ -101,7 +112,7 @@ const cash = Cash.prototype.init as typeof Cash.prototype.init & CashStatic;
 cash.fn = cash.prototype = Cash.prototype; // Ensuring that `cash () instanceof cash`
 
 Cash.prototype.length = 0;
-Cash.prototype.splice = splice; // Ensuring a cash collection gets printed as array-like in Chrome
+Cash.prototype.splice = splice; // Ensuring a cash collection gets printed as array-like in Chrome's devtools
 
 if ( typeof Symbol === 'function' ) {
   Cash.prototype[Symbol['iterator']] = Array.prototype[Symbol['iterator']];
@@ -164,12 +175,14 @@ Cash.prototype.last = function ( this: Cash ) {
 // @require core/cash.ts
 // @require core/variables.ts
 
+type MapCallback<T> = ( this: T, index: number, ele: T ) => Ele;
+
 interface Cash {
-  map ( callback: Function ): Cash;
+  map ( callback: MapCallback<Ele> ): Cash;
 }
 
-Cash.prototype.map = function ( this: Cash, callback: Function ) {
-  return cash ( map.call ( this, ( ele, i ) => callback.call ( ele, i, ele ) ) );
+Cash.prototype.map = function ( this: Cash, callback: MapCallback<Ele> ) {
+  return cash ( map.call ( this, ( ele: Ele, i: number ) => callback.call ( ele, i, ele ) ) );
 };
 
 
@@ -189,11 +202,11 @@ Cash.prototype.slice = function ( this: Cash ) {
 
 const dashAlphaRe = /-([a-z])/g;
 
-function camelCaseReplace ( all, letter ) {
+function camelCaseReplace ( match: string, letter: string ): string {
   return letter.toUpperCase ();
 }
 
-function camelCase ( str: string ) {
+function camelCase ( str: string ): string {
   return str.replace ( dashAlphaRe, camelCaseReplace );
 }
 
@@ -206,7 +219,9 @@ cash.camelCase = camelCase;
 
 // @require ./cash.ts
 
-function each ( arr: ArrayLike<any>, callback: Function ): void {
+type EachCallback<T> = ( this: T, index: number, ele: T ) => any;
+
+function each<T> ( arr: ArrayLike<T>, callback: EachCallback<T> ): void {
 
   for ( let i = 0, l = arr.length; i < l; i++ ) {
 
@@ -217,7 +232,7 @@ function each ( arr: ArrayLike<any>, callback: Function ): void {
 }
 
 interface CashStatic {
-  each ( arr: ArrayLike<any>, callback: Function ): void;
+  each<T> ( arr: ArrayLike<T>, callback: EachCallback<T> ): void;
 }
 
 cash.each = each;
@@ -227,10 +242,10 @@ cash.each = each;
 // @require core/each.ts
 
 interface Cash {
-  each ( callback: Function ): this;
+  each ( callback: EachCallback<Ele> ): this;
 }
 
-Cash.prototype.each = function ( this: Cash, callback: Function ) {
+Cash.prototype.each = function ( this: Cash, callback: EachCallback<Ele> ) {
   each ( this, callback );
   return this;
 };
@@ -250,13 +265,13 @@ Cash.prototype.removeProp = function ( this: Cash, prop: string ) {
 
 // @require ./cash.ts
 
-function extend ( target, ...objs: any[] ) {
+function extend ( target: any, ...objs: any[] ) {
 
-  let args = arguments,
-      length = args.length;
+  const args = arguments,
+        length = args.length;
 
   for ( let i = ( length < 2 ? 0 : 1 ); i < length; i++ ) {
-    for ( let key in args[i] ) {
+    for ( const key in args[i] ) {
       target[key] = args[i][key];
     }
   }
@@ -274,7 +289,7 @@ Cash.prototype.extend = function ( plugins: plainObject ) {
 };
 
 interface CashStatic {
-  extend ( target, ...objs: any[] );
+  extend ( target: any, ...objs: any[] ): any;
 }
 
 cash.extend = extend;
@@ -282,27 +297,25 @@ cash.extend = extend;
 
 // @require ./cash.ts
 
-let guid = 1;
-
 interface CashStatic {
   guid: number;
 }
 
-cash.guid = guid;
+cash.guid = 1;
 
 
 // @require ./cash.ts
 
-function matches ( ele: HTMLElement, selector: string ): boolean {
+function matches ( ele: any, selector: string ): boolean {
 
-  const matches = ele && ( ele.matches || ele['webkitMatchesSelector'] || ele['mozMatchesSelector'] || ele['msMatchesSelector'] || ele['oMatchesSelector'] );
+  const matches = ele && ( ele['matches'] || ele['webkitMatchesSelector'] || ele['mozMatchesSelector'] || ele['msMatchesSelector'] || ele['oMatchesSelector'] );
 
   return !!matches && matches.call ( ele, selector );
 
 }
 
 interface CashStatic {
-  matches ( ele: HTMLElement, selector: string ): boolean;
+  matches ( ele: any, selector: string ): boolean;
 }
 
 cash.matches = matches;
@@ -310,9 +323,9 @@ cash.matches = matches;
 
 // @require ./variables.ts
 
-function pluck ( arr: ArrayLike<any>, prop: string, deep?: boolean ): ArrayLike<any> {
+function pluck<T> ( arr: ArrayLike<T>, prop: string, deep?: boolean ): Array<T> {
 
-  const plucked = [];
+  const plucked: Array<T> = [];
 
   for ( let i = 0, l = arr.length; i < l; i++ ) {
 
@@ -337,31 +350,45 @@ function pluck ( arr: ArrayLike<any>, prop: string, deep?: boolean ): ArrayLike<
 
 // @require ./cash.ts
 
-function isCash ( x ): x is Cash {
+function isCash ( x: any ): x is Cash {
   return x instanceof Cash;
 }
 
-function isFunction ( x ): x is Function {
+function isWindow ( x: any ): x is Window {
+  return !!x && x === x.window;
+}
+
+function isDocument ( x: any ): x is Document {
+  return !!x && x.nodeType === 9;
+}
+
+function isElement ( x: any ): x is HTMLElement {
+  return !!x && x.nodeType === 1;
+}
+
+function isFunction ( x: any ): x is Function {
   return typeof x === 'function';
 }
 
-function isString ( x ): x is string {
+function isString ( x: any ): x is string {
   return typeof x === 'string';
 }
 
-function isNumeric ( x ): boolean {
+function isNumeric ( x: any ): boolean {
   return !isNaN ( parseFloat ( x ) ) && isFinite ( x );
 }
 
 const {isArray} = Array;
 
 interface CashStatic {
-  isFunction ( x ): x is Function;
-  isString ( x ): x is string;
-  isNumeric ( x ): boolean;
-  isArray ( x ): x is Array<any>;
+  isWindow ( x: any ): x is Window;
+  isFunction ( x: any ): x is Function;
+  isString ( x: any ): x is string;
+  isNumeric ( x: any ): boolean;
+  isArray ( x: any ): x is Array<any>;
 }
 
+cash.isWindow = isWindow;
 cash.isFunction = isFunction;
 cash.isString = isString;
 cash.isNumeric = isNumeric;
@@ -373,12 +400,12 @@ cash.isArray = isArray;
 // @require collection/each.ts
 
 interface Cash {
-  prop ( prop: string );
-  prop ( prop: string, value ): this;
+  prop ( prop: string ): any;
+  prop ( prop: string, value: any ): this;
   prop ( props: plainObject ): this;
 }
 
-Cash.prototype.prop = function ( this: Cash, prop: string | plainObject, value? ) {
+Cash.prototype.prop = function ( this: Cash, prop: string | plainObject, value?: any ) {
 
   if ( !prop ) return;
 
@@ -390,7 +417,7 @@ Cash.prototype.prop = function ( this: Cash, prop: string | plainObject, value?
 
   }
 
-  for ( let key in prop ) {
+  for ( const key in prop ) {
 
     this.prop ( key, prop[key] );
 
@@ -407,12 +434,12 @@ Cash.prototype.prop = function ( this: Cash, prop: string | plainObject, value?
 function getCompareFunction ( comparator: Comparator ): Function {
 
   return isString ( comparator )
-           ? ( i, ele ) => matches ( ele, comparator )
+           ? ( i: number, ele: Ele ) => matches ( ele, comparator )
            : isFunction ( comparator )
              ? comparator
              : isCash ( comparator )
-               ? ( i, ele ) => comparator.is ( ele )
-               : ( i, ele ) => ele === comparator;
+               ? ( i: number, ele: Ele ) => comparator.is ( ele )
+               : ( i: number, ele: Ele ) => ele === comparator;
 
 }
 
@@ -433,7 +460,7 @@ Cash.prototype.filter = function ( this: Cash, comparator: Comparator ) {
 
   const compare = getCompareFunction ( comparator );
 
-  return cash ( filter.call ( this, ( ele, i ) => compare.call ( ele, i, ele ) ) );
+  return cash ( filter.call ( this, ( ele: Ele, i: number ) => compare.call ( ele, i, ele ) ) );
 
 };
 
@@ -463,7 +490,7 @@ interface Cash {
 }
 
 Cash.prototype.hasClass = function ( this: Cash, cls: string ) {
-  return cls && some.call ( this, ele => ele.classList.contains ( cls ) );
+  return cls && some.call ( this, ( ele: Ele ) => ele.classList.contains ( cls ) );
 };
 
 
@@ -496,15 +523,17 @@ Cash.prototype.removeAttr = function ( this: Cash, attr: string ) {
 // @require ./remove_attr.ts
 
 interface Cash {
-  attr ( attrs: string );
-  attr ( attrs: string, value ): this;
+  attr (): undefined;
+  attr ( attrs: string ): string | null;
+  attr ( attrs: string, value: string ): this;
   attr ( attrs: plainObject ): this;
 }
 
-function attr ( this: Cash, attr: string );
-function attr ( this: Cash, attr: string, value ): Cash;
+function attr ( this: Cash ): undefined;
+function attr ( this: Cash, attr: string ): string | null;
+function attr ( this: Cash, attr: string, value: string ): Cash;
 function attr ( this: Cash, attr: plainObject ): Cash;
-function attr ( this: Cash, attr: string | plainObject, value? ) {
+function attr ( this: Cash, attr?: string | plainObject, value?: string ) {
 
   if ( !attr ) return;
 
@@ -520,13 +549,15 @@ function attr ( this: Cash, attr: string | plainObject, value? ) {
 
     }
 
+    if ( value === undefined ) return this;
+
     if ( value === null ) return this.removeAttr ( attr );
 
     return this.each ( ( i, ele ) => { ele.setAttribute ( attr, value ) } );
 
   }
 
-  for ( let key in attr ) {
+  for ( const key in attr ) {
 
     this.attr ( key, attr[key] );
 
@@ -589,7 +620,7 @@ interface Cash {
 }
 
 Cash.prototype.removeClass = function ( this: Cash, cls?: string ) {
-  return !arguments.length ? this.attr ( 'class', '' ) : this.toggleClass ( cls as string, false );
+  return !arguments.length ? this.attr ( 'class', '' ) : this.toggleClass ( cls, false );
 };
 
 
@@ -606,12 +637,12 @@ Cash.prototype.removeClass = function ( this: Cash, cls?: string ) {
 // @require ./cash.ts
 // @require ./variables
 
-function unique ( arr: ArrayLike<any> ): ArrayLike<any> {
-  return arr.length > 1 ? filter.call ( arr, ( item, index, self ) => indexOf.call ( self, item ) === index ) : arr;
+function unique<T> ( arr: ArrayLike<T> ): ArrayLike<T> {
+  return arr.length > 1 ? filter.call ( arr, ( item: T, index: number, self: ArrayLike<T> ) => indexOf.call ( self, item ) === index ) : arr;
 }
 
 interface CashStatic {
-  unique ( arr: ArrayLike<any> ): ArrayLike<any>;
+  unique<T> ( arr: ArrayLike<T> ): ArrayLike<T>;
 }
 
 cash.unique = unique;
@@ -630,11 +661,12 @@ Cash.prototype.add = function ( this: Cash, selector: Selector, context?: Contex
 };
 
 
+// @require core/type_checking.ts
 // @require core/variables.ts
 
-function computeStyle ( ele: HTMLElement, prop: string, isVariable?: boolean ): undefined | string {
+function computeStyle ( ele: Ele, prop: string, isVariable?: boolean ): string | undefined {
 
-  if ( ele.nodeType !== 1 || !prop ) return;
+  if ( !isElement ( ele ) || !prop ) return;
 
   const style = win.getComputedStyle ( ele, null );
 
@@ -645,7 +677,7 @@ function computeStyle ( ele: HTMLElement, prop: string, isVariable?: boolean ):
 
 // @require ./compute_style.ts
 
-function computeStyleInt ( ele: HTMLElement, prop: string ): number {
+function computeStyleInt ( ele: Ele, prop: string ): number {
 
   return parseInt ( computeStyle ( ele, prop ), 10 ) || 0;
 
@@ -670,7 +702,7 @@ function isCSSVariable ( prop: string ): boolean {
 // @require core/variables.ts
 // @require ./is_css_variable.ts
 
-const prefixedProps: plainObject = {},
+const prefixedProps: { [prop: string]: string } = {},
       {style} = div,
       vendorsPrefixes = ['webkit', 'moz', 'ms', 'o'];
 
@@ -707,7 +739,7 @@ cash.prefixedProp = getPrefixedProp;
 // @require core/type_checking.ts
 // @require ./is_css_variable.ts
 
-const numericProps = {
+const numericProps: { [prop: string]: true | undefined } = {
   animationIterationCount: true,
   columnCount: true,
   flexGrow: true,
@@ -721,7 +753,7 @@ const numericProps = {
   zIndex: true
 };
 
-function getSuffixedValue ( prop: string, value: number | string, isVariable: boolean = isCSSVariable ( prop ) ): number | string {
+function getSuffixedValue ( prop: string, value: string, isVariable: boolean = isCSSVariable ( prop ) ): string {
 
   return !isVariable && !numericProps[prop] && isNumeric ( value ) ? `${value}px` : value;
 
@@ -737,15 +769,15 @@ function getSuffixedValue ( prop: string, value: number | string, isVariable: bo
 // @require ./helpers/is_css_variable.ts
 
 interface Cash {
-  css ( prop: string );
-  css ( prop: string, value ): this;
+  css ( prop: string ): string | undefined;
+  css ( prop: string, value: string ): this;
   css ( props: plainObject ): this;
 }
 
-function css ( this: Cash, prop: string );
-function css ( this: Cash, prop: string, value ): Cash;
+function css ( this: Cash, prop: string ): string | undefined;
+function css ( this: Cash, prop: string, value: string ): Cash;
 function css ( this: Cash, prop: plainObject ): Cash;
-function css ( this: Cash, prop: string | plainObject, value? ) {
+function css ( this: Cash, prop: string | plainObject, value?: string ) {
 
   if ( isString ( prop ) ) {
 
@@ -761,11 +793,11 @@ function css ( this: Cash, prop: string | plainObject, value? ) {
 
     return this.each ( ( i, ele ) => {
 
-      if ( ele.nodeType !== 1 ) return;
+      if ( !isElement ( ele ) ) return;
 
       if ( isVariable ) {
 
-        ele.style.setProperty ( prop, value );
+        ele.style.setProperty ( prop as string, value ); //TSC
 
       } else {
 
@@ -777,7 +809,7 @@ function css ( this: Cash, prop: string | plainObject, value? ) {
 
   }
 
-  for ( let key in prop ) {
+  for ( const key in prop ) {
 
     this.css ( key, prop[key] );
 
@@ -795,7 +827,7 @@ Cash.prototype.css = css;
 
 // @require core/camel_case.ts
 
-function getData ( ele: HTMLElement, key: string ) {
+function getData ( ele: Ele, key: string ): any {
 
   const value = ele.dataset ? ele.dataset[key] || ele.dataset[camelCase ( key )] : ele.getAttribute ( `data-${key}` );
 
@@ -810,7 +842,7 @@ function getData ( ele: HTMLElement, key: string ) {
 
 // @require core/camel_case.ts
 
-function setData ( ele: HTMLElement, key: string, value ): void {
+function setData ( ele: Ele, key: string, value: any ): void {
 
   try {
     value = JSON.stringify ( value );
@@ -841,22 +873,22 @@ const dataAttributeRe = /^data-(.+)/;
 
 interface Cash {
   data (): plainObject | undefined;
-  data ( name: string );
-  data ( name: string, value ): this;
+  data ( name: string ): any;
+  data ( name: string, value: any ): this;
   data ( datas: plainObject ): this;
 }
 
 function data ( this: Cash ): plainObject | undefined;
-function data ( this: Cash, name: string );
-function data ( this: Cash, name: string, value ): Cash;
+function data ( this: Cash, name: string ): any;
+function data ( this: Cash, name: string, value: any ): Cash;
 function data ( this: Cash, name: plainObject ): Cash;
-function data ( this: Cash, name?: string | plainObject, value? ) {
+function data ( this: Cash, name?: string | plainObject, value?: any ) {
 
   if ( !name ) {
 
     if ( !this[0] ) return;
 
-    const datas = {};
+    const datas: { [data: string]: any } = {};
 
     each ( this[0].attributes, ( i, attr ) => {
 
@@ -880,7 +912,7 @@ function data ( this: Cash, name?: string | plainObject, value? ) {
 
   }
 
-  for ( let key in name ) {
+  for ( const key in name ) {
 
     this.data ( key, name[key] );
 
@@ -898,27 +930,28 @@ Cash.prototype.data = data;
 
 // @require css/helpers/compute_style_int.ts
 
-function getExtraSpace ( ele: HTMLElement, xAxis?: boolean ): number {
+function getExtraSpace ( ele: Element, xAxis?: boolean ): number {
   return computeStyleInt ( ele, `border${ xAxis ? 'Left' : 'Top' }Width` ) + computeStyleInt ( ele, `padding${ xAxis ? 'Left' : 'Top' }` ) + computeStyleInt ( ele, `padding${ xAxis ? 'Right' : 'Bottom' }` ) + computeStyleInt ( ele, `border${ xAxis ? 'Right' : 'Bottom' }Width` );
 }
 
 
 // @require core/cash.ts
 // @require core/each.ts
+// @require core/type_checking.ts
 // @require core/variables.ts
 
 interface Cash {
-  innerWidth (): number;
-  innerHeight (): number;
+  innerWidth (): number | undefined;
+  innerHeight (): number | undefined;
 }
 
-each ( ['Width', 'Height'], ( i, prop: string ) => {
+each ( ['Width', 'Height'], ( i, prop: 'Width' | 'Height' ) => {
 
-  Cash.prototype[`inner${prop}`] = function () {
+  Cash.prototype[`inner${prop}`] = function ( this: Cash ) {
 
     if ( !this[0] ) return;
 
-    if ( this[0] === win ) return win[`inner${prop}`];
+    if ( isWindow ( this[0] ) ) return win[`inner${prop}`];
 
     return this[0][`client${prop}`];
 
@@ -930,6 +963,7 @@ each ( ['Width', 'Height'], ( i, prop: string ) => {
 // @require core/camel_case.ts
 // @require core/cash.ts
 // @require core/each.ts
+// @require core/type_checking.ts
 // @require core/variables.ts
 // @require css/helpers/compute_style.ts
 // @require css/helpers/get_suffixed_value.ts
@@ -942,25 +976,25 @@ interface Cash {
   height ( value: number | string ): this;
 }
 
-each ( ['width', 'height'], ( index: number, prop: string ) => {
+each ( ['width', 'height'], ( index: number, prop: 'width' | 'height' ) => {
 
-  Cash.prototype[prop] = function ( value?: number | string ) {
+  Cash.prototype[prop] = function ( this: Cash, value?: number | string ) {
 
     if ( !this[0] ) return value === undefined ? undefined : this;
 
     if ( !arguments.length ) {
 
-      if ( this[0] === win ) return this[0][ camelCase ( `outer-${prop}` )];
+      if ( isWindow ( this[0] ) ) return this[0][ camelCase ( `outer-${prop}` )];
 
       return this[0].getBoundingClientRect ()[prop] - getExtraSpace ( this[0], !index );
 
     }
 
-    const valueNumber = parseInt ( value as string, 10 );
+    const valueNumber = parseInt ( value as string, 10 ); //TSC
 
     return this.each ( ( i, ele ) => {
 
-      if ( ele.nodeType !== 1 ) return;
+      if ( !isElement ( ele ) ) return;
 
       const boxSizing = computeStyle ( ele, 'boxSizing' );
 
@@ -975,6 +1009,7 @@ each ( ['width', 'height'], ( index: number, prop: string ) => {
 
 // @require core/cash.ts
 // @require core/each.ts
+// @require core/type_checking.ts
 // @require core/variables.ts
 // @require css/helpers/compute_style_int.ts
 
@@ -985,11 +1020,11 @@ interface Cash {
 
 each ( ['Width', 'Height'], ( index: number, prop: string ) => {
 
-  Cash.prototype[`outer${prop}`] = function ( includeMargins?: boolean ) {
+  Cash.prototype[`outer${prop}`] = function ( this: Cash, includeMargins?: boolean ) {
 
     if ( !this[0] ) return;
 
-    if ( this[0] === win ) return win[`outer${prop}`];
+    if ( isWindow ( this[0] ) ) return win[`outer${prop}`];
 
     return this[0][`offset${prop}`] + ( includeMargins ? computeStyleInt ( this[0], `margin${ !index ? 'Left' : 'Top' }` ) + computeStyleInt ( this[0], `margin${ !index ? 'Right' : 'Bottom' }` ) : 0 );
 
@@ -1005,7 +1040,7 @@ each ( ['Width', 'Height'], ( index: number, prop: string ) => {
 
 // @require css/helpers/compute_style.ts
 
-const defaultDisplay = {};
+const defaultDisplay: { [tagName: string]: string } = {};
 
 function getDefaultDisplay ( tagName: string ): string {
 
@@ -1026,7 +1061,7 @@ function getDefaultDisplay ( tagName: string ): string {
 
 // @require css/helpers/compute_style.ts
 
-function isHidden ( ele: HTMLElement ): boolean {
+function isHidden ( ele: Element ): boolean {
 
   return computeStyle ( ele, 'display' ) === 'none';
 
@@ -1098,21 +1133,21 @@ Cash.prototype.show = function ( this: Cash ) {
 
 function hasNamespaces ( ns1: string[], ns2: string[] ): boolean {
 
-  return !ns2 || !some.call ( ns2, ns => ns1.indexOf ( ns ) < 0 );
+  return !ns2 || !some.call ( ns2, ( ns: string ) => ns1.indexOf ( ns ) < 0 );
 
 }
 
 
 const eventsNamespace = '__cashEvents',
       eventsNamespacesSeparator = '.',
-      eventsFocus = { focus: 'focusin', blur: 'focusout' },
-      eventsHover = { mouseenter: 'mouseover', mouseleave: 'mouseout' },
+      eventsFocus: { [event: string]: string | undefined } = { focus: 'focusin', blur: 'focusout' },
+      eventsHover: { [event: string]: string | undefined } = { mouseenter: 'mouseover', mouseleave: 'mouseout' },
       eventsMouseRe = /^(?:mouse|pointer|contextmenu|drag|drop|click|dblclick)/i;
 
 
 // @require ./variables.ts
 
-function getEventNameBubbling ( name: string ) {
+function getEventNameBubbling ( name: string ): string {
 
   return eventsHover[name] || eventsFocus[name] || name;
 
@@ -1121,7 +1156,7 @@ function getEventNameBubbling ( name: string ) {
 
 // @require ./variables.ts
 
-function getEventsCache ( ele: Ele ): plainObject {
+function getEventsCache ( ele: Ele ): { [event: string]: [string[], string, EventCallback][] } {
 
   return ele[eventsNamespace] = ( ele[eventsNamespace] || {} );
 
@@ -1131,16 +1166,16 @@ function getEventsCache ( ele: Ele ): plainObject {
 // @require core/guid.ts
 // @require events/helpers/get_events_cache.ts
 
-function addEvent ( ele: Ele, name: string, namespaces: string[], selector: string, callback: Function ): void {
+function addEvent ( ele: Ele, name: string, namespaces: string[], selector: string, callback: EventCallback ): void {
 
-  callback['guid'] = ( callback['guid'] || guid++ );
+  callback.guid = callback.guid || cash.guid++;
 
   const eventCache = getEventsCache ( ele );
 
   eventCache[name] = ( eventCache[name] || [] );
   eventCache[name].push ([ namespaces, selector, callback ]);
 
-  ele.addEventListener ( name, callback as EventListener ); //TSC
+  ele.addEventListener ( name, callback );
 
 }
 
@@ -1160,7 +1195,7 @@ function parseEventName ( eventName: string ): [string, string[]] {
 // @require ./has_namespaces.ts
 // @require ./parse_event_name.ts
 
-function removeEvent ( ele: Ele, name?: string, namespaces?: string[], selector?: string, callback?: Function ): void {
+function removeEvent ( ele: Ele, name?: string, namespaces?: string[], selector?: string, callback?: EventCallback ): void {
 
   const cache = getEventsCache ( ele );
 
@@ -1178,7 +1213,7 @@ function removeEvent ( ele: Ele, name?: string, namespaces?: string[], selector?
 
     cache[name] = cache[name].filter ( ([ ns, sel, cb ]) => {
 
-      if ( ( callback && cb['guid'] !== callback['guid'] ) || !hasNamespaces ( ns, namespaces ) || ( selector && selector !== sel ) ) return true;
+      if ( ( callback && cb.guid !== callback.guid ) || !hasNamespaces ( ns, namespaces ) || ( selector && selector !== sel ) ) return true;
 
       ele.removeEventListener ( name, cb );
 
@@ -1200,11 +1235,11 @@ function removeEvent ( ele: Ele, name?: string, namespaces?: string[], selector?
 interface Cash {
   off (): this;
   off ( events: string ): this;
-  off ( events: string, callback: Function ): this;
-  off ( events: string, selector: string, callback: Function ): this;
+  off ( events: string, callback: EventCallback ): this;
+  off ( events: string, selector: string, callback: EventCallback ): this;
 }
 
-Cash.prototype.off = function ( this: Cash, eventFullName?: string, selector?: string | Function, callback?: Function ) {
+Cash.prototype.off = function ( this: Cash, eventFullName?: string, selector?: string | EventCallback, callback?: EventCallback ) {
 
   if ( eventFullName === undefined ) {
 
@@ -1249,18 +1284,18 @@ Cash.prototype.off = function ( this: Cash, eventFullName?: string, selector?: s
 
 interface Cash {
   on ( events: plainObject ): this;
-  on ( events: string, callback: Function, _one?: boolean ): this;
-  on ( events: string, selector: string | Function, callback: Function, _one?: boolean ): this;
+  on ( events: string, callback: EventCallback, _one?: boolean ): this;
+  on ( events: string, selector: string | EventCallback, callback: EventCallback, _one?: boolean ): this;
 }
 
 function on ( this: Cash, eventFullName: plainObject ): Cash;
-function on ( this: Cash, eventFullName: string, callback: Function, _one?: boolean ): Cash;
-function on ( this: Cash, eventFullName: string, selector: string | Function, callback: Function, _one?: boolean ): Cash;
-function on ( this: Cash, eventFullName: string | plainObject, selector?: string | Function, callback?: boolean | Function, _one?: boolean ) {
+function on ( this: Cash, eventFullName: string, callback: EventCallback, _one?: boolean ): Cash;
+function on ( this: Cash, eventFullName: string, selector: string | EventCallback, callback: EventCallback, _one?: boolean ): Cash;
+function on ( this: Cash, eventFullName: string | plainObject, selector?: string | EventCallback, callback?: boolean | EventCallback, _one?: boolean ) {
 
   if ( !isString ( eventFullName ) ) {
 
-    for ( let key in eventFullName ) {
+    for ( const key in eventFullName ) {
 
       this.on ( key, selector, eventFullName[key] );
 
@@ -1283,11 +1318,11 @@ function on ( this: Cash, eventFullName: string | plainObject, selector?: string
 
     this.each ( ( i, ele ) => {
 
-      const finalCallback = function ( event ) {
+      const finalCallback = function ( event: EventObj ) {
 
         if ( event.namespace && !hasNamespaces ( namespaces, event.namespace.split ( eventsNamespacesSeparator ) ) ) return;
 
-        let thisArg = ele;
+        let thisArg: EventTarget = ele;
 
         if ( selector ) {
 
@@ -1295,7 +1330,7 @@ function on ( this: Cash, eventFullName: string | plainObject, selector?: string
 
           while ( !matches ( target, selector as string ) ) { //TSC
             if ( target === ele ) return;
-            target = target.parentNode;
+            target = target['parentNode'];
             if ( !target ) return;
           }
 
@@ -1316,7 +1351,7 @@ function on ( this: Cash, eventFullName: string | plainObject, selector?: string
 
         }
 
-        const returnValue = ( callback as Function ).call ( thisArg, event, event.data ); //TSC
+        const returnValue = ( callback as EventCallback ).call ( thisArg, event, event.data ); //TSC
 
         if ( _one ) {
 
@@ -1333,7 +1368,7 @@ function on ( this: Cash, eventFullName: string | plainObject, selector?: string
 
       };
 
-      finalCallback['guid'] = callback['guid'] = ( callback['guid'] || guid++ );
+      finalCallback.guid = callback['guid'] = ( callback['guid'] || cash.guid++ ); //TSC
 
       addEvent ( ele, name, namespaces, selector as string, finalCallback ); //TSC
 
@@ -1353,15 +1388,15 @@ Cash.prototype.on = on;
 
 interface Cash {
   one ( events: plainObject ): this;
-  one ( events: string, callback: Function ): this;
-  one ( events: string, selector: string | Function, callback: Function ): this;
+  one ( events: string, callback: EventCallback ): this;
+  one ( events: string, selector: string | EventCallback, callback: EventCallback ): this;
 }
 
 function one ( this: Cash, eventFullName: plainObject ): Cash;
-function one ( this: Cash, eventFullName: string, callback: Function ): Cash;
-function one ( this: Cash, eventFullName: string, selector: string | Function, callback: Function ): Cash;
-function one ( this: Cash, eventFullName: string | plainObject, selector?: string | Function, callback?: Function ) {
-  return this.on ( ( eventFullName as string ), selector, callback, true ); //TSC
+function one ( this: Cash, eventFullName: string, callback: EventCallback ): Cash;
+function one ( this: Cash, eventFullName: string, selector: string | EventCallback, callback: EventCallback ): Cash;
+function one ( this: Cash, eventFullName: string | plainObject, selector?: string | EventCallback, callback?: EventCallback ) {
+  return this.on ( eventFullName as string, selector, callback, true ); //TSC
 };
 
 Cash.prototype.one = one;
@@ -1401,12 +1436,12 @@ Cash.prototype.ready = function ( this: Cash, callback: Function ) {
 // @require ./helpers/variables.ts
 
 interface Cash {
-  trigger ( event: string | Event, data? ): this;
+  trigger ( event: Event | string, data?: any ): this;
 }
 
-Cash.prototype.trigger = function ( this: Cash, eventFullName: string | Event, data? ) {
+Cash.prototype.trigger = function ( this: Cash, eventFullName: Event | string, data?: any ) {
 
-  let evt: string | Event = eventFullName;
+  let evt: EventObj;
 
   if ( isString ( eventFullName ) ) {
 
@@ -1415,19 +1450,23 @@ Cash.prototype.trigger = function ( this: Cash, eventFullName: string | Event, d
 
     evt = doc.createEvent ( type );
     evt.initEvent ( name, true, true );
-    evt['namespace'] = namespaces.join ( eventsNamespacesSeparator );
+    evt.namespace = namespaces.join ( eventsNamespacesSeparator );
+
+  } else {
+
+    evt = eventFullName;
 
   }
 
-  evt['data'] = data;
+  evt.data = data;
 
-  const isEventFocus = ( evt['type'] in eventsFocus );
+  const isEventFocus = ( evt.type in eventsFocus );
 
   return this.each ( ( i, ele ) => {
 
-    if ( isEventFocus && isFunction ( ele[evt['type']] ) ) {
+    if ( isEventFocus && isFunction ( ele[evt.type] ) ) {
 
-      ele[evt['type']]();
+      ele[evt.type]();
 
     } else {
 
@@ -1450,9 +1489,9 @@ Cash.prototype.trigger = function ( this: Cash, eventFullName: string | Event, d
 // @require core/pluck.ts
 // @require core/variables.ts
 
-function getValue ( ele ): string | string[] {
+function getValue ( ele: Ele ): string | string[] {
 
-  if ( ele.multiple ) return pluck ( filter.call ( ele.options, option => option.selected && !option.disabled && !option.parentNode.disabled ), 'value' ) as string[];
+  if ( ele.multiple ) return pluck ( filter.call ( ele.options, option => option.selected && !option.disabled && !option.parentNode.disabled ), 'value' );
 
   return ele.value || '';
 
@@ -1518,7 +1557,7 @@ Cash.prototype.serialize = function ( this: Cash ) {
 
 interface Cash {
   val (): string | string[];
-  val ( value ): this;
+  val ( value: string | string[] ): this;
 }
 
 function val ( this: Cash ): string | string[];
@@ -1661,9 +1700,7 @@ interface Cash {
 
 Cash.prototype.empty = function ( this: Cash ) {
 
-  const ele = this[0];
-
-  if ( ele ) {
+  return this.each ( ( i, ele ) => {
 
     while ( ele.firstChild ) {
 
@@ -1671,9 +1708,7 @@ Cash.prototype.empty = function ( this: Cash ) {
 
     }
 
-  }
-
-  return this;
+  });
 
 };
 
@@ -1826,7 +1861,6 @@ Cash.prototype.position = function ( this: Cash ) {
 // @require core/unique.ts
 // @require core/variables.ts
 // @require collection/each.ts
-// @require collection/filter.ts
 
 interface Cash {
   children ( comparator?: Comparator ): Cash;
@@ -1834,9 +1868,13 @@ interface Cash {
 
 Cash.prototype.children = function ( this: Cash, comparator?: Comparator ) {
 
-  let result: Ele[] | Cash = [];
+  const result: Ele[] = [];
+
+  this.each ( ( i, ele ) => {
+
+    push.apply ( result, ele.children );
 
-  this.each ( ( i, ele ) => { push.apply ( result, ele.children ) } );
+  });
 
   return filtered ( cash ( unique ( result ) ), comparator );
 
@@ -1853,7 +1891,7 @@ interface Cash {
 
 Cash.prototype.contents = function ( this: Cash ) {
 
-  let result: Ele[] = [];
+  const result: Ele[] = [];
 
   this.each ( ( i, ele ) => {
 
@@ -1891,18 +1929,17 @@ Cash.prototype.find = function ( this: Cash, selector: string ) {
 };
 
 
-// @require collection/filter.ts
 // @require collection/filter.ts
 // @require traversal/find.ts
 
 const scriptTypeRe = /^$|^module$|\/(?:java|ecma)script/i,
       HTMLCDATARe = /^\s*<!(?:\[CDATA\[|--)|(?:\]\]|--)>\s*$/g;
 
-function evalScripts ( node: Node ) {
+function evalScripts ( node: Node ): void {
 
   const collection = cash ( node );
 
-  collection.filter ( 'script' ).add ( collection.find ( 'script' ) ).each ( ( i, ele ) => {
+  collection.filter ( 'script' ).add ( collection.find ( 'script' ) ).each ( ( i, ele: HTMLScriptElement ) => {
     if ( !ele.src && scriptTypeRe.test ( ele.type ) ) { // The script type is supported
       if ( ele.ownerDocument.documentElement.contains ( ele ) ) { // The element is attached to the DOM // Using `documentElement` for broader browser support
         eval ( ele.textContent.replace ( HTMLCDATARe, '' ) );
@@ -1915,7 +1952,7 @@ function evalScripts ( node: Node ) {
 
 // @require ./eval_scripts.ts
 
-function insertElement ( anchor: Node, child: Node, prepend?: boolean, prependTarget?: Node ): void {
+function insertElement ( anchor: Ele, child: Ele, prepend?: boolean, prependTarget?: Element ): void {
 
   if ( prepend ) {
 
@@ -1938,8 +1975,8 @@ function insertElement ( anchor: Node, child: Node, prepend?: boolean, prependTa
 
 function insertContent ( parent: Cash, child: Cash, prepend?: boolean ): void {
 
-  each ( parent, ( index: number, parentEle: HTMLElement ) => {
-    each ( child, ( i, childEle: HTMLElement ) => {
+  each ( parent, ( index: number, parentEle: Ele ) => {
+    each ( child, ( i, childEle: Ele ) => {
       insertElement ( parentEle, !index ? childEle : childEle.cloneNode ( true ), prepend, prepend && parentEle.firstChild );
     });
   });
@@ -1986,7 +2023,7 @@ interface Cash {
 
 Cash.prototype.insertAfter = function ( this: Cash, selector: Selector ) {
 
-  cash ( selector ).each ( ( index: number, ele: HTMLElement ) => {
+  cash ( selector ).each ( ( index: number, ele: Ele ) => {
 
     const parent = ele.parentNode;
 
@@ -2031,7 +2068,7 @@ interface Cash {
 
 Cash.prototype.insertBefore = function ( this: Cash, selector: Selector ) {
 
-  cash ( selector ).each ( ( index: number, ele: HTMLElement ) => {
+  cash ( selector ).each ( ( index: number, ele: Ele ) => {
 
     const parent = ele.parentNode;
 
@@ -2137,7 +2174,7 @@ Cash.prototype.wrapAll = function ( this: Cash, selector?: Selector ) {
 
     this.first ().before ( structure );
 
-    let wrapper = structure[0] as Element;
+    let wrapper = structure[0];
 
     while ( wrapper.children.length ) wrapper = wrapper.firstElementChild;
 
@@ -2227,8 +2264,8 @@ interface Cash {
 Cash.prototype.has = function ( this: Cash, selector: string | HTMLElement ) {
 
   const comparator = isString ( selector )
-                       ? ( i, ele ) => !!find ( selector, ele ).length
-                       : ( i, ele ) => ele.contains ( selector );
+                       ? ( i: number, ele: Ele ) => !!find ( selector, ele ).length
+                       : ( i: number, ele: Ele ) => ele.contains ( selector );
 
   return this.filter ( comparator );
 
@@ -2428,7 +2465,9 @@ Cash.prototype.prevAll = function ( this: Cash, comparator?: Comparator ) {
 
 // @require core/cash.ts
 // @require core/filtered.ts
-// @require collection/filter.ts
+// @require core/unique.ts
+// @require core/variables.ts
+// @require collection/each.ts
 // @require ./children.ts
 // @require ./parent.ts
 
@@ -2438,9 +2477,15 @@ interface Cash {
 
 Cash.prototype.siblings = function ( this: Cash, comparator?: Comparator ) {
 
-  const ele = this[0];
+  const result: Ele[] = [];
 
-  return filtered ( this.parent ().children ().filter ( ( i, child ) => child !== ele ), comparator );
+  this.each ( ( i, ele ) => {
+
+    push.apply ( result, cash ( ele ).parent ().children ( ( ci, child ) => child !== ele ) );
+
+  });
+
+  return filtered ( cash ( unique ( result ) ), comparator );
 
 };
 
diff --git a/package.json b/package.json
index 0a3d2590..073feb3d 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "cash-dom",
   "description": "An absurdly small jQuery alternative for modern browsers.",
-  "version": "4.0.0",
+  "version": "4.1.0",
   "license": "MIT",
   "main": "./dist/cash.js",
   "module": "./dist/cash.esm.js",