Using AngularJS Upgrade (ngUpgrade) for migration

Migrating from AngularJS to Angular (2+) can be a complex and time-consuming process, especially when dealing with large applications. However, the ngUpgrade library provides an efficient solution for this by allowing AngularJS and Angular (2+) code to coexist within the same application during the transition. This enables incremental migration, where you can migrate parts of the application gradually instead of a full rewrite, making the process more manageable.

Here’s an in-depth guide on how to use ngUpgrade for migration:

What is ngUpgrade?

ngUpgrade is a library provided by Angular that facilitates the coexistence of AngularJS and Angular components, directives, and services. It helps you to:

Run both AngularJS and Angular code in the same application.
Migrate AngularJS components to Angular incrementally.
Mix AngularJS and Angular components in the same template.
Reuse AngularJS services in Angular and vice versa.

This approach enables you to move your app from AngularJS to Angular progressively, reducing the risk of downtime and ensuring that you can continue developing new features while migrating the old ones.

Steps to Migrate Using ngUpgrade

To use ngUpgrade for migration, follow these steps:

1. Prepare the AngularJS Application

Before integrating Angular with AngularJS, make sure your AngularJS application is ready for migration. This includes:

Ensuring the application is working well and has been updated to the latest AngularJS version (1.7.x is ideal, as it provides the most features for ngUpgrade).
Identifying key parts of the application that you want to migrate, such as modules, services, or components.

2. Set Up Angular and AngularJS in the Same Application

To start using ngUpgrade, you need to install both Angular and AngularJS in your project. Follow these steps:

Install Angular and AngularJS: You’ll need to install both Angular (2+) and AngularJS via npm. bashCopyEditnpm install @angular/core @angular/upgrade @angular/platform-browser-dynamic angular --save
- @angular/upgrade: This package provides the necessary APIs for upgrading your AngularJS app to Angular.
- angular: This installs AngularJS (1.x), which is required to run AngularJS alongside Angular.

3. Set Up the Angular Module and Bootstrap

To start using both Angular and AngularJS together, you’ll need to create an Angular Module and bootstrap both frameworks. Here’s how to set it up:

Create an Angular Module: Define an Angular module where you will initialize the upgrade process. typescriptCopyEditimport { NgModule } from '@angular/core'; import { BrowserModule } from '@angular/platform-browser'; import { UpgradeModule } from '@angular/upgrade/static'; @NgModule({ imports: [ BrowserModule, UpgradeModule ], bootstrap: [] }) export class AppModule { }
Bootstrap AngularJS Application within Angular: Use the UpgradeModule to bootstrap the AngularJS app inside the Angular app. In your main.ts (or app.ts for older Angular versions), use the following code to bootstrap both Angular and AngularJS: typescriptCopyEditimport { platformBrowserDynamic } from '@angular/platform-browser-dynamic'; import { UpgradeModule } from '@angular/upgrade/static'; import { AppModule } from './app.module'; import * as angular from 'angular'; import { downgradeComponent } from '@angular/upgrade/static'; const upgradeAdapter = new UpgradeModule(); // Bootstrapping AngularJS app within Angular angular.module('angularJsApp', []) .directive('ngApp', downgradeComponent({ component: YourAngularComponent })); platformBrowserDynamic().bootstrapModule(AppModule) .then((ref) => { upgradeAdapter.bootstrap(document.body, ['angularJsApp'], { strictDi: true }); });
- Here, downgradeComponent is used to downgrade Angular components to AngularJS directives so that they can be used in AngularJS templates.

4. Downgrade Angular Components to AngularJS

As part of the migration, you may want to reuse existing Angular components within your AngularJS application. The ngUpgrade library provides a mechanism to downgrade Angular components to AngularJS directives.

To downgrade an Angular component, you can use the downgradeComponent function.

Example:

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

@Component({
  selector: 'app-angular-component',
  template: '<h1>Hello from Angular</h1>'
})
export class AngularComponent {}

angular.module('angularJsApp')
  .directive('appAngularComponent', downgradeComponent({ component: AngularComponent }));

In this case:

AngularComponent is the Angular component you want to use inside your AngularJS app.
downgradeComponent makes the Angular component usable as a directive in AngularJS.

5. Upgrade AngularJS Components to Angular

Once you’ve downgraded your Angular components to AngularJS, the next step is upgrading AngularJS components or services to Angular. This involves converting AngularJS controllers or services to Angular classes and using Angular’s dependency injection system.

You can use upgradeComponent and upgradeInjectable to upgrade AngularJS components and services to Angular.

Example of upgrading an AngularJS component:

import { Component } from '@angular/core';
import { UpgradeComponent } from '@angular/upgrade/static';

@Component({
  selector: 'app-angularjs-component',
  template: '<h2>Hello from AngularJS component!</h2>'
})
export class AngularJSComponent extends UpgradeComponent {
  constructor(elementRef: ElementRef, injector: Injector) {
    super('angularJsComponent', elementRef, injector);
  }
}

angular.module('angularJsApp')
  .component('angularJsComponent', {
    template: '<h2>Hello from AngularJS!</h2>'
  });

In this case, the AngularJS component is upgraded and used in the Angular app.

6. Transition Services Gradually

Services are one of the easiest parts of the application to migrate. You can use Angular’s dependency injection (DI) system to inject AngularJS services into Angular components and vice versa.

Here’s how you can upgrade an AngularJS service to Angular:

AngularJS service:angular.module('angularJsApp') .service('dataService', function() { this.getData = function() { return 'Data from AngularJS service'; }; });
Upgrade the service to Angular: import { Injectable } from '@angular/core'; import { UpgradeService } from '@angular/upgrade/static'; @Injectable() export class AngularService { constructor(private upgradeService: UpgradeService) {} getData() { const dataService = this.upgradeService.$injector.get('dataService'); return dataService.getData(); } }

7. Migrate Features Incrementally

One of the main advantages of ngUpgrade is that it allows you to migrate features incrementally. You don’t need to rewrite everything at once. This makes the migration process more manageable and allows you to keep the app functional during the transition.

8. Handle Routing Between AngularJS and Angular

When both frameworks are used together, you will need to manage routing between AngularJS and Angular. Use the ngUpgrade library to bridge the two routers and enable smooth transitions between the AngularJS and Angular routes.