Multiple versions of AngularJS and Angular causing conflicts

When you are upgrading an AngularJS application to Angular (Angular 2+), it’s common to run into conflicts if both versions are used simultaneously. This can happen because AngularJS and Angular operate on different architectures, and having multiple versions running at the same time in the same application can cause issues related to routing, services, directives, and dependency injection.

Here is a comprehensive step-by-step guide to help resolve issues when you encounter multiple versions of AngularJS and Angular in the same application.

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Step 1: Understanding the Conflict Between AngularJS and Angular

1.1 AngularJS (1.x) vs Angular (2+)

• AngularJS (1.x) is based on a scope-based architecture with a two-way data binding model.
• Angular (2+) introduced a completely different architecture using components, services, and TypeScript. It does not rely on $scope and introduces features like RxJS, observables, and dependency injection.

When both versions are used in parallel, the following conflicts may occur:

• Routing: Angular uses its own router (@angular/router), whereas AngularJS uses ngRoute or ui-router. These routers may conflict when trying to handle navigation.
• Dependency Injection (DI): Angular has its own DI system that is not compatible with AngularJS’s DI system.
• Controllers, Directives, and Components: Angular uses class-based components, while AngularJS uses controllers and directives. This can cause problems when trying to migrate elements gradually.
• Services: Angular’s services are different from AngularJS’s services, so using both in the same app might lead to issues with injection and sharing state.

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Step 2: Using ngUpgrade for Hybrid Applications

The best approach for handling both AngularJS and Angular in the same application is to use ngUpgrade. This is a tool that allows you to run both versions together and gradually migrate your application to Angular.

2.1 Steps to Set Up ngUpgrade

ngUpgrade provides a set of tools to facilitate running AngularJS and Angular components together. Here’s a general outline of the setup:

1. Install the ngUpgrade Package:

First, you need to install @angular/upgrade to allow both AngularJS and Angular to run in the same application:

npm install @angular/upgrade

2. Bootstrap Hybrid App:

You need to bootstrap both AngularJS and Angular together. You can do this by manually bootstrapping the AngularJS app and using the Angular UpgradeModule to bootstrap Angular components inside the AngularJS application.

Example:

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

@NgModule({
  imports: [UpgradeModule],  // Add UpgradeModule to your Angular module
})
export class AppModule {
  constructor(private upgrade: UpgradeModule) {}

  ngDoBootstrap() {
    this.upgrade.bootstrap(document.body, ['angularjsApp']);  // 'angularjsApp' is the name of your AngularJS module
  }
}

platformBrowserDynamic().bootstrapModule(AppModule);

In the above code:

• The UpgradeModule from Angular helps in bootstrapping both frameworks together.
• The ngDoBootstrap() function is used to initialize the AngularJS app within the Angular app.

3. Using Angular Components in AngularJS:

You can upgrade AngularJS components to Angular components gradually. Use the UpgradeComponent to wrap your Angular components and use them inside AngularJS templates.

Example:

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

angular.module('angularjsApp').directive('angularComponent', downgradeComponent({
  component: AngularComponent
}));

In this case:

• downgradeComponent is used to wrap an Angular component (e.g., AngularComponent) so that it can be used within the AngularJS application.

4. Use Angular Services in AngularJS:

To use Angular services in AngularJS, you can use the downgradeInjectable function. This allows you to inject Angular services into your AngularJS code.

import { downgradeInjectable } from '@angular/upgrade/static';
import { AngularService } from './angular-service';

angular.module('angularjsApp').factory('angularService', downgradeInjectable(AngularService));

5. Handle Routing Conflicts:

Since both AngularJS and Angular have their own routers, you need to handle routing in a way that both can function in parallel.

Approach 1: Use AngularJS for Routing and Angular for Components

• In this case, AngularJS handles the routing and views, and Angular takes care of the components and services. This setup is useful when you want to migrate incrementally.

Approach 2: Migrate Routing Gradually

• If you are migrating your application gradually, you may want to migrate routes one at a time. Use Angular Router for new routes and keep using AngularJS routing for legacy routes. You can configure both to work side-by-side.

2.2 Gradual Migration Approach

You don’t need to migrate the entire app at once. ngUpgrade allows you to upgrade parts of the app incrementally:

• Upgrade Directives: Upgrade AngularJS directives into Angular components and use downgradeComponent to make them compatible.
• Upgrade Services: Migrate AngularJS services to Angular services and use downgradeInjectable to access them in AngularJS.
• Upgrade Routes: Gradually migrate routes from AngularJS to Angular using the Angular Router.

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Step 3: Dealing with Specific Issues and Conflicts

During the migration, you may encounter some specific issues related to both versions running together. Below are common issues and their solutions.

3.1 Dependency Injection Conflicts

Angular and AngularJS have different dependency injection mechanisms. If you are trying to inject AngularJS services into Angular components (or vice versa), you need to be careful about how dependencies are managed.

Solution:

• Use downgradeInjectable and downgradeComponent for Angular services and components.
• Ensure that both frameworks use the correct ngModule for Angular components and ngInject for AngularJS services.

3.2 Controller and Component Conflicts

Angular uses class-based components, whereas AngularJS uses controllers. When upgrading, you need to wrap AngularJS controllers in Angular components and services.

Solution:

• Use the downgradeComponent for Angular components and wrap them in AngularJS directives or controllers.
• Refactor AngularJS controllers to Angular components with lifecycle hooks like ngOnInit instead of $scope methods.

3.3 Performance Degradation

Running both AngularJS and Angular in the same application can cause performance degradation, especially with large applications. This is due to the additional overhead of running two frameworks at the same time.

Solution:

• Minimize the number of components that are still in AngularJS.
• Ensure that AngularJS code only interacts with Angular through ngUpgrade components and services.
• Consider progressively migrating the app and stopping AngularJS code after the migration is complete.

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Step 4: Testing and Finalizing Migration

Once you’ve migrated part of the app and resolved conflicts, test the application thoroughly for issues with:

• Routing: Ensure that both AngularJS and Angular routing are working as expected.
• Data Binding: Ensure that data flows correctly between AngularJS controllers and Angular components.
• Services: Test if services are being injected correctly across both frameworks.
• Performance: Monitor the app’s performance and ensure no significant issues with loading time or responsiveness.

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Step 5: Completing the Migration

Once the migration is complete, you can completely remove AngularJS from the application. At this point:

1. Uninstall AngularJS from the project.
2. Refactor all services and components to Angular.
3. Remove ngUpgrade and any other hybrid app-related code.

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Conclusion

Running multiple versions of AngularJS and Angular in the same application can be challenging, but using ngUpgrade and following a gradual migration process will help ensure smooth transitions. Carefully refactor services, components, and routing to work together, test your app thoroughly, and once the migration is complete, remove AngularJS entirely for a fully Angular-based application.

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Tags

angularjs, angular, ngUpgrade, hybrid app, component migration, downgradeComponent, downgradeInjectable, angular routing, dependency injection, migration strategy