Allow value equality checker to be overridden

Author: HeroicEric

README.md

@@ -97,6 +97,20 @@ var buffer = ObjectProxy.extend(BufferedMixin).create({
 // same as above
 ```
 
+You can also customize the function that is used to determine equality between
+values:
+
+```js
+const CustomBufferedProxy = BufferedProxy.extend({
+  isEqual(a, b, key) {
+    if (key === 'foo') {
+      return customComparisonFn(a, b);
+    } else {
+      return this._super(...arguments);
+    }
+  }
+};
+```
 
 ## development
 

addon/mixin.js

@@ -67,13 +67,13 @@ export default Ember.Mixin.create({
 
     previous = hasOwnProp.call(buffer, key) ? buffer[key] : current;
 
-    if (previous === value) {
+    if (this.isEqual(previous, value, key)) {
       return;
     }
 
     this.propertyWillChange(key);
 
-    if (current === value) {
+    if (this.isEqual(current, value, key)) {
       delete buffer[key];
       if (empty(buffer)) {
         set(this, 'hasBufferedChanges', false);
@@ -141,5 +141,31 @@ export default Ember.Mixin.create({
     }
 
     return false;
+  },
+
+  /**
+    Determines if two values are equal.
+    This is used to determine if a value being set is equal to the buffered
+    value. This is also used to determine if the value being set is equal to the value
+    in the underlying content.
+
+    This can be overriden if you wish to do a custom value comparison:
+
+    ```js
+    const CustomBufferedProxy = BufferedProxy.extend({
+      isEqual(a, b, key) {
+        if (key === 'foo') {
+          return customComparisonFn(a, b);
+        } else {
+          return this._super(...arguments);
+        }
+      }
+    };
+    ```
+
+    @return {Boolean}
+  */
+  isEqual(a, b) {
+    return a === b;
   }
 });

tests/unit/mixin-test.js

@@ -211,3 +211,24 @@ test('that .hasChanged() works', (assert) => {
   assert.equal(proxy.hasChanged(), false, 'Not passing a key returns false');
   assert.equal(proxy.hasChanged('baz'), false, 'If the key does not exist on the proxy then return false');
 });
+
+test('that a custom isEqual works', (assert) => {
+  const BufferedProxy = Ember.ObjectProxy.extend(Mixin, {
+    isEqual(a, b, key) {
+      if (key === 'fooArray') {
+        return a.every(item => b.includes(item));
+      } else {
+        return this._super(...arguments);
+      }
+    }
+  });
+
+  const content = { fooArray: [1, 2, 3], barArray: [1, 2, 3] };
+  const proxy = BufferedProxy.create({ content });
+
+  set(proxy, 'fooArray', [1, 2, 3]);
+  set(proxy, 'barArray', [1, 2, 3]);
+
+  assert.equal(proxy.hasChanged('fooArray'), false, 'custom equality checker works with arrays');
+  assert.equal(proxy.hasChanged('barArray'), true, 'default equality check does not work with arrays');
+});