AngularJS Differences

"AngularJS" and "Angular" share a team, a name and some vocabulary, which is exactly why interviewers ask how they differ. The short version: Angular is not a newer AngularJS, it is a different framework. ## Naming and status - **AngularJS** is the name for every **1.x** version. - **Angular** is everything from version 2 onwards; v22 is current in 2026. - **AngularJS reached end of support in January 2022.** It receives no fixes, including security fixes. - There is no in-place update from one to the other. The official route is a **hybrid app** with `@angular/upgrade`, which is itself in maintenance mode, taking only security fixes. ## The building blocks | Concern | AngularJS (1.x) | Angular | | :-- | :-- | :-- | | Language | JavaScript | TypeScript | | UI unit | Controllers plus templates, directives; `.component()` added later in 1.x | Components (a class with `@Component` and a template), directives, pipes | | Data for the view | Properties on a `$scope` object, often inherited from parent scopes | Fields and signals on the component class | | Data flow | Two-way binding by default (`ng-model` and directive bindings) | One-way by default: `[property]` in, `(event)` out; two-way is opt-in (`[(...)]`, `model()`) | | Keeping the view in sync | **Digest cycle**: re-run all watchers until values stop changing | **Change detection**: check the component tree top-down, then stop | | Dependency injection | Services looked up by string name; array annotations to survive minification | Hierarchical injectors; tokens are classes or `InjectionToken`s; `inject()` | | Modules | `angular.module('app', [...])` for registration | Standalone components by default since v19; `NgModule` still supported | | Templates | `ng-if`, `ng-repeat`, `ng-click`, `{{ }}` | `@if`, `@for`, `(click)`, `[prop]`, `{{ }}`, compiled ahead of time | ## Why the rewrite happened Three limits of AngularJS drove it: 1. **Performance of the digest cycle.** Every binding adds a watcher, and a digest runs all of them, repeatedly, until the page is stable. Large screens with thousands of bindings became slow, and two-way bindings could trigger cascades of extra passes. 2. **Scope inheritance was hard to reason about.** Nested `$scope`s inherited prototypally, so a child could read, shadow or accidentally write a parent's value. 3. **Tooling and scale.** String-named DI, runtime template compilation and plain JavaScript made large codebases hard to refactor and optimise. Angular answered with ahead-of-time compiled templates, TypeScript, one-way data flow, and a change-detection pass that walks the component tree once per cycle. ## What stayed recognisable - **Dependency injection** as the core design idea, now hierarchical and type-based. - **Declarative templates** with `{{ }}` interpolation. - **Directives** as a way to add behaviour to elements. - **Services** as singletons holding shared logic. This familiarity is why hybrid migrations work at all: the concepts map, even though the APIs do not. ## What interviewers listen for - Saying "Angular 2 was an upgrade of AngularJS" misses that it was a rewrite. - Describing Angular's change detection as "a digest loop" imports the AngularJS model: Angular checks the tree once, and in development mode a second verification pass throws `ExpressionChangedAfterItHasBeenCheckedError` (NG0100) instead of looping. - Treating AngularJS as merely "old but fine" ignores that since January 2022 it gets no security patches. ## Migration options in one line each - **Rewrite**: build the Angular app separately and switch over; clean, but a long freeze on the old app. - **Hybrid**: run both with `@angular/upgrade` and move one screen or service at a time. - **Replace gradually at the route level**: serve some routes from a new app; simpler plumbing, but two apps to operate. Which one fits depends on the app's size and test coverage; the hybrid route is the one Angular provides tools for.