diff --git a/js/date.altimpl.ts b/js/date.altimpl.ts
new file mode 100644
index 0000000..5f90723
--- /dev/null
+++ b/js/date.altimpl.ts
@@ -0,0 +1,142 @@
+// alternative implementation
+/**
+ * 计算时间间隔中星期的天数
+ * @param before
+ * @param after
+ * @returns [总天数, 周一天数, 周二天数, 周三天数, 周四天数, 周五天数, 周六天数, 周日天数]
+ */
+export function getWeekday(
+  before: Date,
+  after: Date,
+): [number, number, number, number, number, number, number, number] {
+  if (before > after) {
+    throw new Error('before cannot > after');
+  }
+
+  let weekdayall = 0;
+  let weekday1 = 0;
+  let weekday2 = 0;
+  let weekday3 = 0;
+  let weekday4 = 0;
+  let weekday5 = 0;
+  let weekday6 = 0;
+  let weekday7 = 0;
+  // 获取 before 的第一时间
+  const beforeDay = new Date(
+    `${before.getFullYear()}-${before.getMonth() + 1}-${before.getDate()}`,
+  );
+  // 获取 after 的最后时间
+  const afterDay = new Date(
+    `${after.getFullYear()}-${after.getMonth() + 1}-${after.getDate()}`,
+  );
+  // 24 * 60 * 60 * 1,000 = 86,400,000 毫秒
+  const MILLISECONDS_ONE_DAY = 86400000;
+
+  // 两个时间中间包含多少天
+  let days = (afterDay.getTime() - beforeDay.getTime()) /
+      MILLISECONDS_ONE_DAY + 1;
+  weekdayall = days;
+
+  // 如果不是从周一开始
+  switch (before.getDay()) {
+    case 2:
+      weekday2++;
+      weekday3++;
+      weekday4++;
+      weekday5++;
+      weekday6++;
+      weekday7++;
+      days -= 6;
+      break;
+    case 3:
+      weekday3++;
+      weekday4++;
+      weekday5++;
+      weekday6++;
+      weekday7++;
+      days -= 5;
+      break;
+    case 4:
+      weekday4++;
+      weekday5++;
+      weekday6++;
+      weekday7++;
+      days -= 4;
+      break;
+    case 5:
+      weekday5++;
+      weekday6++;
+      weekday7++;
+      days -= 3;
+      break;
+    case 6:
+      weekday6++;
+      weekday7++;
+      days -= 2;
+      break;
+    case 0:
+      weekday7++;
+      days -= 1;
+      break;
+    default:
+      break;
+  }
+
+  // 如果不是从周日结束
+  switch (after.getDay()) {
+    case 1:
+      weekday1++;
+      days -= 1;
+      break;
+    case 2:
+      weekday1++;
+      weekday2++;
+      days -= 2;
+      break;
+    case 3:
+      weekday1++;
+      weekday2++;
+      weekday3++;
+      days -= 3;
+      break;
+    case 4:
+      weekday1++;
+      weekday2++;
+      weekday3++;
+      weekday4++;
+      days -= 4;
+      break;
+    case 5:
+      weekday1++;
+      weekday2++;
+      weekday3++;
+      weekday4++;
+      weekday5++;
+      days -= 5;
+      break;
+    case 6:
+      weekday1++;
+      weekday2++;
+      weekday3++;
+      weekday4++;
+      weekday5++;
+      weekday6++;
+      days -= 6;
+      break;
+    default:
+      break;
+  }
+
+  const weeks = Math.floor(days / 7);
+
+  return [
+    weekdayall,
+    weekday1 += weeks,
+    weekday2 += weeks,
+    weekday3 += weeks,
+    weekday4 += weeks,
+    weekday5 += weeks,
+    weekday6 += weeks,
+    weekday7 += weeks,
+  ];
+}
diff --git a/js/date.ts b/js/date.ts
index 352de4c..df82ba4 100644
--- a/js/date.ts
+++ b/js/date.ts
@@ -445,3 +445,52 @@ export function parseDate(
 
   return { y, m, d, h, min, s };
 }
+
+/**
+ * 计算时间间隔中星期的天数
+ * @param before
+ * @param after
+ * @returns [总天数, 周一天数, 周二天数, 周三天数, 周四天数, 周五天数, 周六天数, 周日天数]
+ */
+export function getWeekday(
+  before: Date,
+  after: Date,
+): [number, number, number, number, number, number, number, number] {
+  // 获取 before 的第一时间
+  const beforeDay = new Date(
+    `${before.getFullYear()}-${before.getMonth() + 1}-${before.getDate()}`,
+  );
+  // 获取 after 的最后时间
+  const afterDay = new Date(
+    `${after.getFullYear()}-${after.getMonth() + 1}-${after.getDate()}`,
+  );
+  // 24 * 60 * 60 * 1,000 = 86,400,000 毫秒
+  const MILLISECONDS_ONE_DAY = 86400000;
+
+  /** 两个时间中间包含多少天 */
+  const days = Math.round(
+    (afterDay.getTime() - beforeDay.getTime()) / MILLISECONDS_ONE_DAY,
+  ) + 1;
+
+  const beforeWeekday = before.getDay();
+  const afterWeekday = after.getDay();
+  const weeks = (
+    days - (8 - beforeWeekday) % 7 - afterWeekday
+  ) / 7;
+
+  return [
+    days,
+    (afterWeekday !== 0 ? 1 : 0) + weeks,
+    (beforeWeekday === 2 ? 1 : 0) + (afterWeekday >= 2 ? 1 : 0) + weeks,
+    (beforeWeekday === 2 || beforeWeekday === 3 ? 1 : 0) +
+    (afterWeekday >= 3 ? 1 : 0) +
+    weeks,
+    (beforeWeekday >= 2 && beforeWeekday <= 4 ? 1 : 0) +
+    (afterWeekday >= 4 ? 1 : 0) + weeks,
+    (beforeWeekday >= 2 && beforeWeekday <= 5 ? 1 : 0) +
+    (afterWeekday >= 5 ? 1 : 0) + weeks,
+    (beforeWeekday >= 2 && beforeWeekday <= 6 ? 1 : 0) +
+    (afterWeekday === 6 ? 1 : 0) + weeks,
+    (beforeWeekday !== 1 ? 1 : 0) + weeks,
+  ];
+}
diff --git a/js/hash.ts b/js/hash.ts
index ff3afb2..04e2dd3 100644
--- a/js/hash.ts
+++ b/js/hash.ts
@@ -1,6 +1,21 @@
+/**
+ * 校验或签名数据, 目的在于保护数据不被篡改及确认数据来源可靠.
+ *
+ * 主要有三种方式:
+ *
+ * 1. 非加密.
+ * 2. HMAC 签名.
+ * 3. RSA 签名.
+ */
 import { encode } from "../lib/hex";
 import { decode } from "../lib/base64";
 
+/**
+ * 获取数据散列值
+ * @param algorithm 可选 SHA-1 等算法, 不支持 MD5
+ * @param d 需要计算散列值的数据
+ * @returns 数据的散列值
+ */
 export async function hashString(
   algorithm: "SHA-1" | "SHA-256" | "SHA-512",
   d: string | Uint8Array
@@ -66,7 +81,7 @@ export async function hmac(
  * @param d
  * @returns
  */
-export async function rasSign(
+export async function rsaSign(
   key: {
     hash: 'SHA-256' | 'SHA-512';
     /** secret key */
diff --git a/js/lz-string.ts b/js/lz-string.ts
index fb468b9..16f4ced 100644
--- a/js/lz-string.ts
+++ b/js/lz-string.ts
@@ -14,7 +14,9 @@
 const f = String.fromCharCode;
 const keyStrUriSafe =
   'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-!';
-const baseReverseDic: Record<string, { [key: string]: number }> = {};
+export const keyStrBase64Safe =
+  'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
+  const baseReverseDic: Record<string, { [key: string]: number }> = {};
 
 /**
  * 乱序字符串
diff --git a/js/str.ts b/js/str.ts
index c301a37..83556f3 100644
--- a/js/str.ts
+++ b/js/str.ts
@@ -90,3 +90,33 @@ export function fromUnicodeStr(str: string): string {
   }
   return encoded;
 }
+
+/**
+ * 为文本添加 UTF-8 BOM (for Windows...)
+ * - [Magic Number](https://en.wikipedia.org/wiki/Magic_number_(programming))
+ * - [Byte Order Mark](https://en.wikipedia.org/wiki/Byte_order_mark)
+ * @param v 需要增加 BOM 的文本
+ * @returns
+ */
+export function textWithBOM(v: Uint8Array | string): Uint8Array {
+  let data: Uint8Array;
+  if (typeof v === 'string') {
+    const encoder = new TextEncoder();
+    data = encoder.encode(v);
+  } else {
+    // 避免重复增加 BOM
+    if (v[0] === 239 && v[1] === 187 && v[2] === 191) {
+      return v;
+    }
+    // 基于性能考虑, 不会更严格检查 Uint8Array 有效性
+    data = v;
+  }
+
+  /** EF BB BF */
+  const mn = [239, 187, 191];
+  const u8a = new Uint8Array(data.length + 3); // mn.length is 3
+  u8a.set(mn);
+  u8a.set(data, 3); // mn.length is 3
+
+  return u8a;
+}
diff --git a/ts/error.ts b/ts/error.ts
new file mode 100644
index 0000000..f6e4c31
--- /dev/null
+++ b/ts/error.ts
@@ -0,0 +1,10 @@
+/**
+ * 断言传入值是一个 Error
+ * 常用在错误处理 catch 中.
+ * @param v
+ */
+export function assertError(v: unknown): asserts v is Error {
+  if (!(v instanceof Error)) {
+    throw new TypeError(`should be Error but ${v}`);
+  }
+}