Suggest an edit

Improve this article

Refine the answer for “Difference between AngularJS and Angular”. Your changes go to moderation before they’re published.

Approval required

Content

What you’re changing

Title (EN)

Short answer (EN)

Shown above the full answer for quick recall.

Answer (EN)

**AngularJS (1.x)** and **Angular (2+)** are two different frameworks that share a name but almost nothing else.

## Theory

### TL;DR

- AngularJS (2010): JavaScript + controllers + `$scope`; Angular (2016): TypeScript + components + decorators
- Main difference: `$scope` digest cycle vs Zone.js and a component tree
- AngularJS official support ended December 2021; Angular is active, v18 shipped in 2024
- Google rewrote Angular from scratch in 2016, it is not a version upgrade
- Use AngularJS only for legacy maintenance; Angular for everything new

### Quick Example

```html

<div ng-app="app" ng-controller="MainCtrl">
  <input ng-model="name">
  <p>Hello {{ name }}!</p>
</div>
```

```js
angular.module('app', []).controller('MainCtrl', function($scope) {
  $scope.name = 'World'; // $digest() watches every change
});
```

```typescript
// Angular: component class, no $scope needed
@Component({
  selector: 'app-hello',
  template: `<p>Hello {{ name }}!</p>`
})
export class HelloComponent {
  name = 'World'; // TypeScript class property
}
```

In AngularJS, `$scope` is the shared object between controller and template. Angular replaces this with a class whose properties map directly to the template.

### Key Difference

AngularJS binds a global `$scope` tree to templates and runs `$digest()` cycles to check every watcher for changes. It works for small apps but slows down once the watcher count grows. Angular compiles TypeScript ahead of time (AOT), builds a component tree, and uses Zone.js to know when async operations complete, then checks only the affected branch. With `ChangeDetectionStrategy.OnPush`, it skips branches where `@Input` has not changed. The result is 5-10x smaller bundles and noticeably faster rendering on large apps.

I've seen teams still running AngularJS in 2023 because migration kept getting deprioritized. The digest-loop overhead in those apps was consistently the top performance complaint, especially on dashboards with 500+ bound values.

### When to Use

- Old internal tool, no budget for migration: AngularJS (avoid adding new features)
- New SPA, enterprise app, or mobile-first project: Angular
- Team familiar with TypeScript: Angular (better IDE support and refactoring)
- Already on AngularJS and need to scale: use `ngUpgrade` for incremental migration

### Comparison Table

| Characteristic | AngularJS (1.x) | Angular (2+) |
|---|---|---|
| Released | 2010 | 2016 (full rewrite) |
| Language | JavaScript | TypeScript |
| Data binding | Two-way via `$scope`/digest | One-way `@Input`/`@Output` |
| Architecture | MVC, controllers, directives | Components, modules, services |
| CLI | None (manual bower/gulp) | Angular CLI (`ng generate`, `ng build`) |
| Mobile | Basic (PhoneGap) | Native-ready (Ionic, Cordova) |
| Performance | Digest loop slows on 1000+ watchers | AOT + lazy loading, OnPush detection |
| Support | Ended December 2021 | Active, v18 in 2024 |
| When to use | Legacy maintenance only | New projects, enterprise apps |

### How Angular Handles Change Detection

AngularJS parses HTML for `ng-*` directives, builds a `$scope` tree, then runs `$digest()` repeatedly until no watchers fire. Each iteration is O(n) over all watchers, and the loop can repeat up to 10 times per interaction. Angular takes a different path: the `ngc` compiler pre-builds component templates into JavaScript at build time. Zone.js patches browser APIs like `setTimeout` and `addEventListener` to signal when async work completes. Only then does Angular walk the affected part of the component tree.

### Common Mistakes

**Mutating `$scope` inside a native timer in AngularJS:**

```js
// Bad: no $digest triggered, UI stays stale
setTimeout(function() {
  $scope.items.push('new item');
});

// Fix: wrap in $apply
$scope.$apply(function() {
  $scope.items.push('new item');
});
```

**Overusing `[(ngModel)]` in Angular forms:**

```html

<input [(ngModel)]="user.name">
```

For forms with many fields, use reactive forms with `FormControl` and `patchValue`. Fewer checks, better performance under load.

**Missing module imports in Angular:**

```typescript
@NgModule({
  declarations: [MyComponent]
  // missing: imports: [CommonModule, FormsModule]
})
```

`*ngIf` and `*ngFor` live in `CommonModule`. Forgetting the import gives a confusing template parse error that trips up many juniors.

### Real-World Usage

- Netflix migrated dashboard components from AngularJS to Angular for smaller bundle sizes
- Google Workspace uses Angular modules for feature isolation across large teams
- Delta Airlines uses Angular CLI for their booking SPA
- IBM replaced AngularJS promise chains with Angular + RxJS for reactive forms

### Follow-up Questions

**Q:** Why did Google rewrite Angular instead of updating AngularJS?
**A:** The `$scope`/digest design could not support AOT compilation or server-side rendering without a complete redesign. Starting fresh was the practical choice.

**Q:** What is the `$digest` cycle and why does it slow large apps?
**A:** It loops through all registered watchers, comparing current and previous values. If anything changed, it loops again, up to 10 times. With hundreds of watchers this becomes expensive on every user interaction.

**Q:** How does Zone.js replace `$scope.$apply`?
**A:** Zone.js patches `setTimeout`, `Promise`, and DOM events. Angular uses those patches to know when async work finishes and triggers change detection automatically. In AngularJS you had to call `$apply` manually when running code outside the framework.

**Q:** How do you migrate a large AngularJS app to Angular?
**A:** Use `ngUpgrade` to run both frameworks side by side. Migrate components to Angular one at a time. AngularJS and Angular components communicate during the transition via shared services.

**Q:** What are Angular signals and how do they change things?
**A:** Signals (stable in Angular 18) give fine-grained reactivity without Zone.js. A signal tracks which components depend on it and only re-renders those when the value changes, instead of diffing the full tree.

## Examples

### Hello World in Both Frameworks

```html

<div ng-app="app" ng-controller="MainCtrl">
  <p>{{ message }}</p>
</div>
<script>
  angular.module('app', []).controller('MainCtrl', function($scope) {
    $scope.message = 'Hello from AngularJS'; // controller binds to $scope
  });
</script>
```

```typescript
// Angular: class property replaces $scope
@Component({
  selector: 'app-root',
  template: `<p>{{ message }}</p>`
})
export class AppComponent {
  message = 'Hello from Angular';
}
```

Two syntaxes, two mental models. AngularJS connects controller to view through `$scope`. Angular uses a TypeScript class where properties become template data directly, with no shared mutable object in between.

### Todo List: `ng-repeat` vs `*ngFor`

```html

<ul>
  <li ng-repeat="todo in todos">{{ todo.text }}</li>
</ul>
```

```js
$scope.todos = [{text: 'Buy milk'}];
$scope.todos.push({text: 'Walk dog'}); // $digest detects array change, re-renders list
```

```typescript
// Angular: trackBy prevents unnecessary DOM re-creation
@Component({
  template: `
    <ul>
      <li *ngFor="let todo of todos; trackBy: trackById">{{ todo.text }}</li>
    </ul>
    <input [(ngModel)]="newTodo" (keyup.enter)="add()">
  `
})
export class TodosComponent {
  todos = [{id: 1, text: 'Buy milk'}];
  newTodo = '';

trackById(index: number, todo: {id: number}) { return todo.id; }

add() {
    this.todos.push({id: Date.now(), text: this.newTodo});
    this.newTodo = '';
  }
}
```

`trackBy` tells Angular which `<li>` nodes to reuse when the list updates. Without it, Angular destroys and recreates every element on each change. In AngularJS, any array mutation triggers a full list re-render regardless.

Markdown · drag & drop images · ⌘B / ⌘I shortcuts1143 words

For the reviewer

Note to the moderator (optional)

Visible only to the moderator. Helps review go faster.