Add .hasChanged(key) method (#29)

Add .hasChanged(key) method

Find if an individual key has changed or return false.

Author: thoov

README.md

@@ -37,11 +37,13 @@ buffer.get('hasChanges'); // => false
 buffer.set('firstName', 'Luke');
 buffer.get('firstName'); // => 'Luke'
 buffer.get('content.firstName'); // => 'Kris'
+buffer.hasChanged('firstName'); // => true
 
 buffer.discardBufferedChanges();
 
 buffer.get('firstName'); // => 'Kris'
 buffer.get('content.firstName'); // => 'Kris'
+buffer.hasChanged('firstName'); // => false
 
 // Below demonstrates that applyBufferedChanges and discardBufferedChanges
 // can take an optional array of keys.

addon/mixin.js

@@ -123,5 +123,23 @@ export default Ember.Mixin.create({
     if (empty(get(this, 'buffer'))) {
       set(this, 'hasBufferedChanges', false);
     }
+  },
+
+  /*
+   * Determines if a given key has changed else returns false. Allows individual key lookups where
+   * as hasBufferedChanged only looks at the whole buffer.
+   */
+  hasChanged(key) {
+    const { buffer, content } = getProperties(this, ['buffer', 'content']);
+
+    if (typeof key !== 'string' || typeof get(buffer, key) === 'undefined') {
+      return false;
+    }
+
+    if (get(buffer, key) !== get(content, key)) {
+      return true;
+    }
+
+    return false;
   }
 });

tests/unit/mixin-test.js

@@ -177,3 +177,37 @@ test('allows passing other variables at .create time', (assert) => {
   assert.equal(proxy.get('container'), fakeContainer, 'Proxy didn\'t allow defining container property at create time');
   assert.equal(proxy.get('foo'), 'foo', 'Proxy didn\'t allow setting an arbitrary value at create time');
 });
+
+test('that .hasChanged() works', (assert) => {
+  const BufferedProxy = Ember.ObjectProxy.extend(Mixin);
+  const content = {};
+
+  const proxy = BufferedProxy.create({ content });
+
+  set(proxy, 'foo', 1);
+
+  assert.equal(proxy.hasChanged('foo'), true);
+  assert.equal(proxy.hasChanged('bar'), false);
+
+  set(proxy, 'bar', 1);
+
+  assert.equal(proxy.hasChanged('foo'), true);
+  assert.equal(proxy.hasChanged('bar'), true);
+
+  proxy.applyBufferedChanges(['bar']);
+
+  set(proxy, 'foobar', false);
+
+  assert.equal(proxy.hasChanged('foo'), true);
+  assert.equal(proxy.hasChanged('bar'), false);
+  assert.equal(proxy.hasChanged('foobar'), true);
+
+  proxy.applyBufferedChanges();
+
+  assert.equal(proxy.hasChanged('foo'), false);
+  assert.equal(proxy.hasChanged('bar'), false);
+  assert.equal(proxy.hasChanged('foobar'), false);
+
+  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');
+});