Merge pull request #1178 from GarethOates/storeCancelScope

this._changeHandlers was undefined when calling cancel()

store.js

@@ -111,10 +111,13 @@ assign(Store.prototype, {
 
 	onchange: function(callback) {
 		this._changeHandlers.push(callback);
+
+		var store = this;
+
 		return {
 			cancel: function() {
-				var index = this._changeHandlers.indexOf(callback);
-				if (~index) this._changeHandlers.splice(index, 1);
+				var index = store._changeHandlers.indexOf(callback);
+				if (~index) store._changeHandlers.splice(index, 1);
 			}
 		};
 	},
@@ -163,4 +166,4 @@ assign(Store.prototype, {
 	}
 });
 
-export { Store };
+export { Store };

test/store/index.js

@@ -113,6 +113,15 @@ describe('store', () => {
 		});
 	});
 
+	it('allows user to cancel state change callback', () => {
+		const store = new Store();
+		const handler = store.onchange(() => {});
+
+		assert.doesNotThrow(() => {
+			handler.cancel();
+		}, TypeError, 'this._changeHandlers is undefined');
+	});
+
 	describe('computed', () => {
 		it('computes a property based on data', () => {
 			const store = new Store({