@angular/core

APP_ID

constant

A DI token representing a string ID, used primarily for prefixing application attributes and CSS styles when ViewEncapsulation#Emulated is being used.

  
    const APP_ID: InjectionToken<string>;

A DI token representing a string ID, used primarily for prefixing application attributes and CSS styles when ViewEncapsulation#Emulated is being used.

The token is needed in cases when multiple applications are bootstrapped on a page (for example, using bootstrapApplication calls). In this case, ensure that those applications have different APP_ID value setup. For example:

          bootstrapApplication(ComponentA, {  providers: [    { provide: APP_ID, useValue: 'app-a' },    // ... other providers ...  ]});bootstrapApplication(ComponentB, {  providers: [    { provide: APP_ID, useValue: 'app-b' },    // ... other providers ...  ]});

By default, when there is only one application bootstrapped, you don't need to provide the APP_ID token (the ng will be used as an app ID).