Migrating from AngularJS to Angular (Angular 2+)

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Migrating from AngularJS to Angular (Angular 2+)

As AngularJS has reached its end-of-life, many developers are moving to Angular (Angular 2+), a more robust framework with improved performance and modern capabilities. This guide covers essential steps, strategies, and best practices for migrating your applications from AngularJS to Angular.

Table of Contents

Why Migrate to Angular

Angular, the successor of AngularJS, offers numerous advantages, including better performance, TypeScript support, a more powerful CLI, and a component-based architecture. Migrating ensures your application stays maintainable, secure, and performant, while providing access to a broader ecosystem and long-term support.

Key Differences Between AngularJS and Angular

Before starting the migration, it’s essential to understand the core differences between AngularJS and Angular:

  • TypeScript: Angular is built with TypeScript, a superset of JavaScript, providing static typing and improved tooling.
  • Component-Based Architecture: Unlike AngularJS’s controller and scope structure, Angular is entirely component-driven, improving modularity and reusability.
  • Dependency Injection: Angular introduces a more sophisticated dependency injection system, improving testability and flexibility.
  • Improved Performance: Angular uses a faster change detection system and Ahead-of-Time (AOT) compilation for better performance.

Migration Strategies

There are two main strategies for migration:

  • Rewrite: Starting from scratch, ideal for smaller applications but can be time-consuming for large projects.
  • Hybrid Approach: Running AngularJS and Angular side by side, using the ngUpgrade library. This allows for gradual migration of components and services.

Preparing for Migration

Preparation is key for a successful migration. Here are some steps to take before starting the migration:

  • Update AngularJS to the latest version to leverage improved compatibility with the ngUpgrade library.
  • Modularize the Application: Break down your AngularJS app into smaller, modular components, if not done already. This makes migrating each component easier.
  • Refactor Code: Simplify your AngularJS code, reduce the use of $scope, and adopt the component-based architecture in preparation for Angular’s component model.

Step-by-Step Migration Guide

Here’s a step-by-step process to migrate your AngularJS application to Angular:

1. Install Angular and Set Up ngUpgrade

Begin by setting up Angular within your AngularJS project and installing ngUpgrade to allow both frameworks to coexist.


npm install @angular/upgrade --save
    

Next, set up your Angular environment, configuring angular.json and tsconfig.json.

2. Bootstrap the Application with ngUpgrade

Configure Angular to run alongside AngularJS by using the hybrid bootstrap provided by ngUpgrade. This allows both frameworks to run simultaneously:


import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { UpgradeModule } from '@angular/upgrade/static';

platformBrowserDynamic().bootstrapModule(AppModule).then(platformRef => {
  const upgrade = platformRef.injector.get(UpgradeModule);
  upgrade.bootstrap(document.body, ['myAngularJSApp']);
});
    

3. Migrate Services First

Angular services are easier to migrate than components, as they generally have fewer dependencies on the DOM. Start by rewriting your services in Angular and use the ngUpgrade adapter to make them available to both frameworks.

4. Gradually Migrate Components

Convert your AngularJS components or directives one by one into Angular components. You can use downgradeComponent to make Angular components available to AngularJS until the entire app is migrated.


import { downgradeComponent } from '@angular/upgrade/static';

angular.module('myAngularJSApp')
  .directive('myComponent', downgradeComponent({ component: MyComponent }));
    

5. Migrate Routing to Angular’s Router

If you are using AngularJS’s ngRoute, start migrating to Angular’s Router. This provides a better structure and additional features. Set up Angular Router as the main routing mechanism and slowly move your routes.

6. Finalize Migration and Clean Up

Once all components and services are migrated, remove the ngUpgrade setup and dependencies, and fully switch to Angular’s bootstrap process. Ensure all configurations are updated and perform thorough testing to verify the application works as expected.

Best Practices for Migration

  • Use TypeScript: Angular relies on TypeScript, so adopt it early in the migration process for better tooling and maintainability.
  • Follow Angular Style Guide: Adhere to Angular’s style guide for consistent and maintainable code.
  • Document Each Step: Document the migration process and changes made to each module or component, helping future maintenance and understanding.

Conclusion

Migrating from AngularJS to Angular (Angular 2+) involves careful planning, understanding key differences, and following a structured migration process. By following these steps and best practices, you can ensure a smooth transition to a modern, powerful framework that will keep your application performant and maintainable for years to come.