global.d.ts

/**
 * The BeforeInstallPromptEvent is fired at the Window.onbeforeinstallprompt handler
 * before a user is prompted to "install" a web site to a home screen on mobile.
 *
 * @deprecated Only supported on Chrome and Android Webview.
 */
interface BeforeInstallPromptEvent extends Event {
  /**
   * Returns an array of DOMString items containing the platforms on which the event was dispatched.
   * This is provided for user agents that want to present a choice of versions to the user such as,
   * for example, "web" or "play" which would allow the user to chose between a web version or
   * an Android version.
   */ 
  readonly platforms: Array<string>;

  /**
   * Returns a Promise that resolves to a DOMString containing either "accepted" or "dismissed".
   */
  readonly userChoice: Promise<{
    outcome: "accepted" | "dismissed";
    platform: string;
  }>;

  /**
   * Allows a developer to show the install prompt at a time of their own choosing.
   * This method returns a Promise.
   */
  prompt(): Promise<{
    outcome: "accepted" | "dismissed";
    platform: string;
  }>;
}

declare global {
  interface WindowEventMap {
    beforeinstallprompt: BeforeInstallPromptEvent;
  }
}