support custom isEqual function

addon/index.js

@@ -34,6 +34,8 @@ export default Ember.Mixin.create({
     this._super(...arguments);
 
     let config = this.get('didChangeAttrsConfig');
+    let equalityFn = config.isEqual || isEqual;
+
     let trackedAttrs = config.attrs;
     let oldValues = this.get('_didChangeAttrsWeakMap').get(this);
     let changes = {};
@@ -43,7 +45,7 @@ export default Ember.Mixin.create({
       let current = this.get(key);
       let previous = oldValues[key];
 
-      if (!isEqual(key, previous, current)) { //TODO: configurable equality fn
+      if (!equalityFn(key, previous, current)) {
         changes[key] = { previous, current };
         oldValues[key] = current;
       }

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

@@ -32,6 +32,7 @@ test('Basic usage', function(assert) {
   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]');
@@ -47,3 +48,63 @@ test('Basic usage', function(assert) {
   this.set('name', 'TheTomster');
   assert.equal(didChangeAttrsCallCount, 1, '`didChangeAttrs` is not called when an untracked attribute is changed');
 });
+
+test('Custom isEqual', function(assert) {
+  let changedAttrs, didChangeAttrsCallCount = 0;
+
+  registerComponent(this, {
+    didChangeAttrsConfig: {
+      attrs: ['user', 'isAdmin'],
+      isEqual(key, a, b) {
+        if (key === 'user') {
+          return (a && b) ? a.id === b.id : a === b;
+        }
+        return a === b;
+      }
+    },
+
+    didChangeAttrs(changes) {
+      this._super(...arguments);
+
+      didChangeAttrsCallCount++;
+      changedAttrs = changes;
+    }
+  });
+
+  this.set('user', { name: 'Tomster', id: '123' });
+  this.set('isAdmin', false);
+
+  this.render(hbs`{{x-changer user=user isAdmin=isAdmin}}`);
+
+  assert.equal(didChangeAttrsCallCount, 0, '`didChangeAttrs` is not called on initial render');
+
+  this.set('user', { name: 'TheTomster', id: '123' });
+
+  assert.equal(didChangeAttrsCallCount, 0, '`didChangeAttrs` is not called because user entities are equal');
+
+  this.set('user', { name: 'Zoey', id: '456' });
+
+  assert.equal(didChangeAttrsCallCount, 1, '`didChangeAttrs` is called because user entities are not equal');
+  assert.deepEqual(changedAttrs, {
+    user: {
+      previous: {
+        id: '123',
+        name: 'Tomster'
+      },
+      current: {
+        id: '456',
+        name: 'Zoey'
+      }
+    }
+  }, '`user` included in `changedAttrs` because `user.id` is different');
+
+  this.set('isAdmin', true);
+
+  assert.equal(didChangeAttrsCallCount, 2, '`didChangeAttrs` is called because isAdmin changed');
+  assert.deepEqual(changedAttrs, {
+    isAdmin: {
+      previous: false,
+      current: true
+    }
+  }, '`isAdmin` included in `changedAttrs` because it changed');
+});