angular-migration

SKILL.md

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,
      useFactory: (i: any) => i.get('oldService'),
      deps: ['$injector']
    }
  ]
})

// Use in Angular
@Component({...})
export class NewComponent {
  constructor(@Inject(OLD_SERVICE) private oldService: any) {
    console.log(this.oldService.getData());
  }
}

Routing Migration

// Before: AngularJS routing
angular.module("myApp").config(function ($routeProvider) {
  $routeProvider
    .when("/users", {
      template: "<user-list></user-list>",
    })
    .when("/users/:id", {
      template: "<user-detail></user-detail>",
    });
});

// After: Angular routing
import { NgModule } from "@angular/core";
import { RouterModule, Routes } from "@angular/router";

const routes: Routes = [
  { path: "users", component: UserListComponent },
  { path: "users/:id", component: UserDetailComponent },
];

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule],
})
export class AppRoutingModule {}

Forms Migration

<!-- Before: AngularJS -->
<form name="userForm" ng-submit="saveUser()">
  <input type="text" ng-model="user.name" required />
  <input type="email" ng-model="user.email" required />
  <button ng-disabled="userForm.$invalid">Save</button>
</form>

// After: Angular (Template-driven)
@Component({
  template: `
    <form #userForm="ngForm" (ngSubmit)="saveUser()">
      <input type="text" [(ngModel)]="user.name" name="name" required>
      <input type="email" [(ngModel)]="user.email" name="email" required>
      <button [disabled]="userForm.invalid">Save</button>
    </form>
  `
})

// Or Reactive Forms (preferred)
import { FormBuilder, FormGroup, Validators } from '@angular/forms';

@Component({
  template: `
    <form [formGroup]="userForm" (ngSubmit)="saveUser()">
      <input formControlName="name">
      <input formControlName="email">
      <button [disabled]="userForm.invalid">Save</button>
    </form>
  `
})
export class UserFormComponent {
  userForm: FormGroup;

  constructor(private fb: FormBuilder) {
    this.userForm = this.fb.group({
      name: ['', Validators.required],
      email: ['', [Validators.required, Validators.email]]
    });
  }

  saveUser() {
    console.log(this.userForm.value);
  }
}

Migration Timeline

Phase 1: Setup (1-2 weeks)
- Install Angular CLI
- Set up hybrid app
- Configure build tools
- Set up testing

Phase 2: Infrastructure (2-4 weeks)
- Migrate services
- Migrate utilities
- Set up routing
- Migrate shared components

Phase 3: Feature Migration (varies)
- Migrate feature by feature
- Test thoroughly
- Deploy incrementally

Phase 4: Cleanup (1-2 weeks)
- Remove AngularJS code
- Remove ngUpgrade
- Optimize bundle
- Final testing