shortcut$

shortcut-manager.ts

  shortcut$(...shortcutKeys: ShortcutKey[]): Observable<KeyboardEvent[] | undefined> {
    const keyCodes: string[][] = shortcutKeys.map(shortcutKey => 
          Array.isArray(shortcutKey.keyCode) ? shortcutKey.keyCode : [shortcutKey.keyCode]);
    if (keyCodes.length === 1 && keyCodes[0].length === 1) {
      // small optimization for a single key binding
      return this.singleShortcut$(keyCodes[0]);
    }

    const keyCodesAsCartesianProduct = [...this.cartesianIterator(keyCodes)];
    const arr$: Observable<KeyboardEvent[] | undefined>[] =
          keyCodesAsCartesianProduct.map(k => this.singleShortcut$(k));
    return merge(...arr$);
  }