add DidChangeAttrs mixin

addon/index.js

@@ -1 +1,56 @@
-/* Hey @GavinJoyce, add your code here! :) */
+import WeakMap from 'ember-weakmap';
+import Ember from 'ember';
+
+function isEqual(key, a, b) {
+  return a === b;
+}
+
+export default Ember.Mixin.create({
+  _didChangeAttrsWeakMap: null, //this tracks previous state of any `trackAttrChanges`
+  didChangeAttrsConfig: [], //attributes to track
+
+  didReceiveAttrs() {
+    this._super(...arguments);
+
+    let weakMap = this.get('_didChangeAttrsWeakMap');
+
+    if (weakMap === null) { //first run
+      let config = this.get('didChangeAttrsConfig');
+      let trackedAttrs = config.attrs;
+      let initialValues = {};
+
+      for (let i=0; i<trackedAttrs.length; i++) {
+        let key = trackedAttrs[i];
+        initialValues[key] = this.get(key);
+      }
+
+      weakMap = new WeakMap();
+      weakMap.set(this, initialValues);
+      this.set('_didChangeAttrsWeakMap', weakMap);
+    }
+  },
+
+  didUpdateAttrs() {
+    this._super(...arguments);
+
+    let config = this.get('didChangeAttrsConfig');
+    let trackedAttrs = config.attrs;
+    let oldValues = this.get('_didChangeAttrsWeakMap').get(this);
+    let changes = {};
+
+    for (let i=0; i<trackedAttrs.length; i++) {
+      let key = trackedAttrs[i];
+      let current = this.get(key);
+      let previous = oldValues[key];
+
+      if (!isEqual(key, previous, current)) { //TODO: configurable equality fn
+        changes[key] = { previous, current };
+        oldValues[key] = current;
+      }
+    }
+
+    if(Object.keys(changes).length > 0) {
+      this.didChangeAttrs(changes);
+    }
+  },
+});

tests/integration/did-change-attrs-test.js

@@ -0,0 +1,49 @@
+import Ember from 'ember';
+import { test, moduleForComponent } from 'ember-qunit';
+import hbs from 'htmlbars-inline-precompile';
+import DidChangeAttrs from 'ember-did-change-attrs';
+
+function registerComponent(testSuite, hash, klass = Ember.Component) {
+  testSuite.register('component:x-changer', klass.extend(DidChangeAttrs, hash));
+}
+
+moduleForComponent('x-changer', 'Integration | DidChangeAttrs', {
+  integration: true
+});
+
+test('Basic usage', function(assert) {
+  let changedAttrs, didChangeAttrsCallCount = 0;
+
+  registerComponent(this, {
+    didChangeAttrsConfig: {
+      attrs: ['email', 'isAdmin']
+    },
+
+    didChangeAttrs(changes) {
+      this._super(...arguments);
+
+      didChangeAttrsCallCount++;
+      changedAttrs = changes;
+    }
+  });
+
+  this.set('name', 'Tomster');
+  this.set('email', '[email protected]');
+  this.set('isAdmin', false);
+
+  this.render(hbs`{{x-changer email=email isAdmin=isAdmin name=name}}`);
+  assert.equal(didChangeAttrsCallCount, 0, '`didChangeAttrs` is not called on initial render');
+
+  this.set('email', '[email protected]');
+  assert.equal(didChangeAttrsCallCount, 1, '`didChangeAttrs` is called when an attribute changed');
+
+  assert.deepEqual(changedAttrs, {
+    email: {
+      previous: '[email protected]',
+      current: '[email protected]'
+    }
+  }, '`changedAttrs` contains the attribute changes');
+
+  this.set('name', 'TheTomster');
+  assert.equal(didChangeAttrsCallCount, 1, '`didChangeAttrs` is not called when an untracked attribute is changed');
+});