如何将Angular 1.5代码升级至Angular 5？是否有简便方法或需从零开始？

Hey there! Let’s break down upgrading your Angular 1.5 app to Angular 5—good news: you don’t have to rebuild from scratch. Angular provides a hybrid migration path that lets you run both frameworks side-by-side, so you can upgrade components piece by piece instead of doing a full rewrite all at once. That said, whether you choose incremental migration or a full rebuild depends on your app’s size and codebase quality. Let’s dive into the details:

Do You Need to Start Over? #

For most real-world apps, no—hybrid migration is the way to go. This approach minimizes downtime, lets you keep using your existing working code, and reduces risk. That said, a full rewrite might make sense if:

• Your Angular 1.5 app is tiny with super simple functionality
• The codebase is riddled with technical debt and minimal test coverage
• You want to completely rearchitect the app from the ground up

Step-by-Step Hybrid Migration Guide #

1. Prep Your Angular 1.5 App First #

Clean up your existing code to make migration smoother:

• Update AngularJS to the latest 1.x version (1.8.x is ideal, as it has better hybrid support)
• Refactor messy code into reusable AngularJS 1.5 components (since Angular 5 uses a component-based model too, this will make conversions easier)
• Remove deprecated AngularJS features (like avoiding over-reliance on $scope in favor of controllerAs syntax)
• Ensure all third-party dependencies are up-to-date and compatible with later AngularJS versions

2. Set Up the Hybrid Environment #

This is where you’ll run Angular 1.5 and Angular 5 side-by-side:

• Install Angular 5 and the critical upgrade tool:

  npm install @angular/core@5 @angular/upgrade@5 @angular/platform-browser@5 @angular/common@5
  

• Create an Angular 5 root module that uses UpgradeModule to bootstrap your existing AngularJS app:

  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() {
      // Bootstrap your existing AngularJS module here
      this.upgrade.bootstrap(document.body, ['yourAngularJSAppModule']);
    }
  }
  

• Update your build setup (Webpack, etc.) to bundle both AngularJS and Angular 5 code.

3. Migrate Components & Features Gradually #

Start with small, isolated components (like headers, footers, or simple UI widgets) to get the hang of it:

• Convert AngularJS components to Angular 5:
  • Replace AngularJS component() definitions with Angular 5’s @Component decorator
  • Swap template syntax: ng-repeat → *ngFor, ng-if → *ngIf, two-way binding uses [(ngModel)] (don’t forget to import FormsModule!)
  • Replace $scope/controllerAs with class properties and constructor injection
• Use wrapper utilities if you need to mix components:
  • UpgradeComponent: Wrap an AngularJS component to use it in Angular 5 code
  • downgradeComponent: Wrap an Angular 5 component to use it in remaining AngularJS code
• Migrate services: Convert AngularJS factory()/service() to Angular 5’s @Injectable() services, and use downgradeInjectable to make them available in AngularJS parts of the app.

4. Test & Phase Out AngularJS #

• After migrating each component, run tests to ensure functionality stays intact
• Gradually remove AngularJS dependencies as you migrate more features
• Once all components are converted, you can remove UpgradeModule and fully switch to Angular 5

Key Gotchas to Watch For #

• Template Syntax Differences: Angular 5 has stricter syntax—double-check bindings and directives to avoid errors
• Dependency Injection: Angular 5 uses constructor injection instead of AngularJS’s $inject arrays (though $inject still works for compatibility)
• Routing: Angular 5’s RouterModule replaces AngularJS’s ngRoute or ui-router—you can use hybrid routing temporarily, but plan to migrate routes fully eventually
• Third-Party Libraries: Some AngularJS libraries don’t have Angular 5 equivalents—look for alternatives or wrap them using the upgrade tools

内容的提问来源于stack exchange，提问作者rohit Mukherjee