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Migrating from Ionic 3.0 to Ionic 4.0

The migration from Ionic 3 to Ionic 4 is the most significant in the frameworks history, and it sets a course for Ionic that likely will not be deviated from for years to come.

Migration Ionic 3 to 4

We suggest the following general process when migrating an existing application from Ionic 3 to 4:

  1. Generate a new project using the blank starter
  2. Copy any Angular services from src/providers to src/app/services
    • Services should include { providedIn: 'root' } in the @Injectable() decorator.
  3. Copy the app’s other root level items (pipes, components, etc) keeping in mind that the directory structure changes from src/components to src/app/components, etc.
  4. Copy global Sass styling from src/app/app.scss to src/global.scss
  5. Copy the rest of the application, page by page or feature by feature, keeping the following items in mind:
    • Emulated Shadow DOM is turned on by default
    • Page/component Sass should no longer be wrapped in the page/component tag and should use Angular’s styleUrls option of the @Component decorator
    • RxJS has been updated from v5 to v6
    • Certain lifecycle hooks should be replaced by Angular’s hooks
    • Markup changes may be required
In many cases, using the Ionic CLI to generate a new object and then copying the code also works very well. For example: ionic g service weather will create a shell Weather service and test. The code can then be copied from the older project with minor modifications as needed. This helps to ensure proper structure is followed. This also generates shells for unit tests.

Changes in Package Name

In Ionic 4, the package name is @ionic/angular. Uninstall Ionic 3 and install Ionic 4 using the new package name:

    $ npm uninstall ionic-angular
    $ npm install @ionic/angular

While migrating an app, update the imports from ionic-angular to @ionic/angular.

Project structure

One of the major changes between an Ionic 3 app and an Ionic 4 app is the overall project layout and structure. In v3, Ionic apps had a custom convention for how an app should be setup and what that folder structure should look like. In v4, this has been changed to follow the recommended setup of each supported framework.

For example, if an app is using Angular, that project structure will be exactly what an Angular CLI app would be. This change, while not too difficult to accommodate, helps to keep common patterns and documentation consistent.

The above comparison is an example of a v4 app’s project structure. For developers with experience in a vanilla Angular project, this should feel really familiar.

There is a src/ directory that acts as the home for the app. This includes the index.html, any assets, environment configuration, and any app specific config files.

While migrating an app to take advantage of this new layout, it is suggested that a new project “base” is made with the CLI. Then, with the new project layout, migrate the features of the app piece by piece. Pages/components/etc. should be moved into the src/app/ folder.

Ensure your Ionic configuration file has the appropriate type. The project type for v3 is ionic-angular. The project type for v4 is angular. If this value is incorrect, the CLI may invoke the incorrect build scripts.

See the following ionic.config.json as an example:

  "name": "my-app",
  "type": "angular"

RxJS Changes

Between V3 and V4, RxJS was updated to version 6. This changes many of the import paths of operators and core RxJS functions. Please see the RxJS Migration Guide for details.

Lifecycle Events

With V4, we’re now able to utilize the typical events provided by Angular. But for certain cases, you might want to have access to the events fired when a component has finished animating during it’s route change. In this case, the ionViewWillEnter, ionViewDidEnter, ionViewWillLeave, and ionViewDidLeave have been ported over from V3. Use these events to coordinate actions with Ionic’s own animations system.

Older events like ionViewDidLoad, ionViewCanLeave, and ionViewCanEnter have been removed, and the proper Angular alternatives should be used.

Overlay Components

In prior versions of Ionic, overlay components such as Loading, Toast, or Alert were created synchronously. In Ionic v4, these components are all created asynchronously. As a result of this, the API is now promise-based.

// v3
showAlert() {
  const alert = this.alertCtrl.create({
    message: "Hello There",
    subHeader: "I'm a subheader"


In v4, promises are used:

showAlert() {
    message: "Hello There",
    subHeader: "I'm a subheader"
  }).then(alert => alert.present());

// Or using async/await

async showAlert() {
  const alert = await this.alertCtrl.create({
    message: "Hello There",
    subHeader: "I'm a subheader"

  await alert.present();

Lazy Loading

Since Navigation has changed, the mechanism for lazy loading has also changed in V4.

In v3, a typical lazy loading setup worked like this:

  segment: 'home'
@Component({ ... })
export class HomePage {}

// home.module.ts
  declarations: [HomePage],
  imports: [IonicPageModule.forChild(HomePage)]
export class HomePageModule {}

However, in v4, lazy loading is done via the loadChildren method of the Angular router:

// home.module.ts
  imports: [
    RouterModule.forChild([{ path: '', component: HomePage }])
  declarations: [HomePage]
export class HomePageModule {}

// app.module.ts
  declarations: [AppComponent],
  imports: [
      { path: 'home', loadChildren: './pages/home/home.module#HomePageModule' },
      { path: '', redirectTo: 'home', pathMatch: 'full' }
  bootstrap: [AppComponent]
export class AppModule {}

Markup Changes

Since v4 moved to Custom Elements, there’s been a significant change to the markup for each component. These changes have all been made to follow the Custom Elements spec, and have been documented in a dedicated file on Github.

To help with these markup changes, we’ve released a TSLint-based Migration Tool, which detects issues and can even fix some of them automatically.

For more Information and to build the app using Ionic, Hire Ionic Developer from us as we give you a high-quality product by utilizing all the latest tools and advanced technology. E-mail us any clock at – or Skype us: “hkinfosoft“.

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