APP_ID
A DI Token representing a unique string id assigned to the application by Angular and used primarily for prefixing application attributes and CSS styles when ViewEncapsulation.Emulated is being used.
const APP_ID: InjectionToken<string>;
说明
If you need to avoid randomly generated value to be used as an application id, you can provide a custom value via a DI provider configuring the root Injectorusing this token.
