/angular-migration

name: angular-migration
description: Migrate from AngularJS to Angular using hybrid mode, incremental component rewriting, and dependency injection updates. Use when upgrading AngularJS applications, planning framework migrations, or modernizing legacy Angular code.

Angular Migration

Master AngularJS to Angular migration, including hybrid apps, component conversion, dependency injection changes, and routing migration.

When to Use This Skill

• Migrating AngularJS (1.x) applications to Angular (2+)
• Running hybrid AngularJS/Angular applications
• Converting directives to components
• Modernizing dependency injection
• Migrating routing systems
• Updating to latest Angular versions
• Implementing Angular best practices

Migration Strategies

1. Big Bang (Complete Rewrite)

• Rewrite entire app in Angular
• Parallel development
• Switch over at once
• **Best for:** Small apps, green field projects

2. Incremental (Hybrid Approach)

• Run AngularJS and Angular side-by-side
• Migrate feature by feature
• ngUpgrade for interop
• **Best for:** Large apps, continuous delivery

3. Vertical Slice

• Migrate one feature completely
• New features in Angular, maintain old in AngularJS
• Gradually replace
• **Best for:** Medium apps, distinct features

Hybrid App Setup

// main.ts - Bootstrap hybrid app
import { platformBrowserDynamic } from "@angular/platform-browser-dynamic";
import { UpgradeModule } from "@angular/upgrade/static";
import { AppModule } from "./app/app.module";

platformBrowserDynamic()
  .bootstrapModule(AppModule)
  .then((platformRef) => {
    const upgrade = platformRef.injector.get(UpgradeModule);
    // Bootstrap AngularJS
    upgrade.bootstrap(document.body, ["myAngularJSApp"], { strictDi: true });
  });

// app.module.ts
import { NgModule } from "@angular/core";
import { BrowserModule } from "@angular/platform-browser";
import { UpgradeModule } from "@angular/upgrade/static";

@NgModule({
  imports: [BrowserModule, UpgradeModule],
})
export class AppModule {
  constructor(private upgrade: UpgradeModule) {}

  ngDoBootstrap() {
    // Bootstrapped manually in main.ts
  }
}

Component Migration

AngularJS Controller → Angular Component

// Before: AngularJS controller
angular
  .module("myApp")
  .controller("UserController", function ($scope, UserService) {
    $scope.user = {};

    $scope.loadUser = function (id) {
      UserService.getUser(id).then(function (user) {
        $scope.user = user;
      });
    };

    $scope.saveUser = function () {
      UserService.saveUser($scope.user);
    };
  });

// After: Angular component
import { Component, OnInit } from "@angular/core";
import { UserService } from "./user.service";

@Component({
  selector: "app-user",
  template: `
    <div>
      <h2>{{ user.name }}</h2>
      <button (click)="saveUser()">Save</button>
    </div>
  `,
})
export class UserComponent implements OnInit {
  user: any = {};

  constructor(private userService: UserService) {}

  ngOnInit() {
    this.loadUser(1);
  }

  loadUser(id: number) {
    this.userService.getUser(id).subscribe((user) => {
      this.user = user;
    });
  }

  saveUser() {
    this.userService.saveUser(this.user);
  }
}

AngularJS Directive → Angular Component

// Before: AngularJS directive
angular.module("myApp").directive("userCard", function () {
  return {
    restrict: "E",
    scope: {
      user: "=",
      onDelete: "&",
    },
    template: `
      <div class="card">
        <h3>{{ user.name }}</h3>
        <button ng-click="onDelete()">Delete</button>
      </div>
    `,
  };
});

// After: Angular component
import { Component, Input, Output, EventEmitter } from "@angular/core";

@Component({
  selector: "app-user-card",
  template: `
    <div class="card">
      <h3>{{ user.name }}</h3>
      <button (click)="delete.emit()">Delete</button>
    </div>
  `,
})
export class UserCardComponent {
  @Input() user: any;
  @Output() delete = new EventEmitter<void>();
}

// Usage: <app-user-card [user]="user" (delete)="handleDelete()"></app-user-card>

Service Migration

// Before: AngularJS service
angular.module("myApp").factory("UserService", function ($http) {
  return {
    getUser: function (id) {
      return $http.get("/api/users/" + id);
    },
    saveUser: function (user) {
      return $http.post("/api/users", user);
    },
  };
});

// After: Angular service
import { Injectable } from "@angular/core";
import { HttpClient } from "@angular/common/http";
import { Observable } from "rxjs";

@Injectable({
  providedIn: "root",
})
export class UserService {
  constructor(private http: HttpClient) {}

  getUser(id: number): Observable<any> {
    return this.http.get(`/api/users/${id}`);
  }

  saveUser(user: any): Observable<any> {
    return this.http.post("/api/users", user);
  }
}

Dependency Injection Changes

Downgrading Angular → AngularJS

// Angular service
import { Injectable } from "@angular/core";

@Injectable({ providedIn: "root" })
export class NewService {
  getData() {
    return "data from Angular";
  }
}

// Make available to AngularJS
import { downgradeInjectable } from "@angular/upgrade/static";

angular.module("myApp").factory("newService", downgradeInjectable(NewService));

// Use in AngularJS
angular.module("myApp").controller("OldController", function (newService) {
  console.log(newService.getData());
});

Upgrading AngularJS → Angular

// AngularJS service
angular.module('myApp').factory('oldService', function() {
  return {
    getData: function() {
      return 'data from AngularJS';
    }
  };
});

// Make available to Angular
import { InjectionToken } from '@angular/core';

export const OLD_SERVICE = new InjectionToken<any>('oldService');

@NgModule({
  providers: [
    {
      provide: OLD_SERVICE,
      useFac