fix(AccessKeyed): avoid dirty-checking keyed array access

fixes #289

src/ast.js

@@ -317,7 +317,10 @@ export class AccessKeyed extends Expression {
     if (obj instanceof Object) {
       this.key.connect(binding, scope);
       let key = this.key.evaluate(scope);
-      if (key !== null && key !== undefined) {
+      // observe the property represented by the key as long as it's not an array
+      // being accessed by an integer key which would require dirty-checking.
+      if (key !== null && key !== undefined
+        && !(Array.isArray(obj) && typeof(key) === 'number')) {
         binding.observeProperty(obj, key);
       }
     }

test/access-keyed-observer.spec.js

@@ -267,10 +267,11 @@ describe('AccessKeyedObserver', () => {
       expect(el.value).toBe(obj.array[obj.key]);
     });
 
-    it('responds to property change', done => {
+    it('does not respond to property change', done => {
+      let original = el.value;
       obj.array[obj.key] = 'foo';
       setTimeout(() => {
-        expect(el.value).toBe(obj.array[obj.key]);
+        expect(el.value).toBe(original);
         done();
         }, checkDelay * 2);
     });
@@ -399,10 +400,11 @@ describe('AccessKeyedObserver', () => {
       expect(el.value).toBe(obj.array[obj.key]);
     });
 
-    it('responds to property change', done => {
+    it('does not respond to property change', done => {
+      let original = el.value;
       obj.array[obj.key] = 'foo';
       setTimeout(() => {
-        expect(el.value).toBe(obj.array[obj.key]);
+        expect(el.value).toBe(original);
         done();
         }, checkDelay * 2);
     });

test/ast/access-keyed.spec.js

@@ -1,4 +1,4 @@
-import {AccessKeyed, AccessScope, LiteralString} from '../../src/ast';
+import {AccessKeyed, AccessScope, LiteralString, LiteralPrimitive} from '../../src/ast';
 import {createScopeForTest} from '../../src/scope';
 
 describe('AccessKeyed', () => {
@@ -40,4 +40,26 @@ describe('AccessKeyed', () => {
     scope = createScopeForTest({});
     expect(expression.evaluate(scope, null)).toBe(undefined);
   });
+
+  it('does not observes property in keyed object access when key is number', () => {
+    let scope = createScopeForTest({ foo: { '0': 'hello world' } });
+    let expression = new AccessKeyed(new AccessScope('foo', 0), new LiteralPrimitive(0));
+    expect(expression.evaluate(scope, null)).toBe('hello world');
+    let binding = { observeProperty: jasmine.createSpy('observeProperty') };
+    expression.connect(binding, scope);
+    expect(binding.observeProperty.calls.argsFor(0)).toEqual([scope.bindingContext, 'foo']);
+    expect(binding.observeProperty.calls.argsFor(1)).toEqual([scope.bindingContext.foo, 0]);
+    expect(binding.observeProperty.calls.count()).toBe(2);
+  });
+
+  it('does not observe property in keyed array access when key is number', () => {
+    let scope = createScopeForTest({ foo: ['hello world'] });
+    let expression = new AccessKeyed(new AccessScope('foo', 0), new LiteralPrimitive(0));
+    expect(expression.evaluate(scope, null)).toBe('hello world');
+    let binding = { observeProperty: jasmine.createSpy('observeProperty') };
+    expression.connect(binding, scope);
+    expect(binding.observeProperty.calls.argsFor(0)).toEqual([scope.bindingContext, 'foo']);
+    expect(binding.observeProperty).not.toHaveBeenCalledWith(scope.bindingContext.foo, 0);
+    expect(binding.observeProperty.calls.count()).toBe(1);
+  });
 });