@ionic/core/components/hardware-back-button.js

/*!
 * (C) Ionic http://ionicframework.com - MIT License
 */
/**
 * When hardwareBackButton: false in config,
 * we need to make sure we also block the default
 * webview behavior. If we don't then it will be
 * possible for users to navigate backward while
 * an overlay is still open. Additionally, it will
 * give the appearance that the hardwareBackButton
 * config is not working as the page transition
 * will still happen.
 */
const blockHardwareBackButton = () => {
  document.addEventListener('backbutton', () => { }); // tslint:disable-line
};
const startHardwareBackButton = () => {
  const doc = document;
  let busy = false;
  doc.addEventListener('backbutton', () => {
    if (busy) {
      return;
    }
    let index = 0;
    let handlers = [];
    const ev = new CustomEvent('ionBackButton', {
      bubbles: false,
      detail: {
        register(priority, handler) {
          handlers.push({ priority, handler, id: index++ });
        }
      }
    });
    doc.dispatchEvent(ev);
    const executeAction = async (handlerRegister) => {
      try {
        if (handlerRegister && handlerRegister.handler) {
          const result = handlerRegister.handler(processHandlers);
          if (result != null) {
            await result;
          }
        }
      }
      catch (e) {
        console.error(e);
      }
    };
    const processHandlers = () => {
      if (handlers.length > 0) {
        let selectedHandler = {
          priority: Number.MIN_SAFE_INTEGER,
          handler: () => undefined,
          id: -1
        };
        handlers.forEach(handler => {
          if (handler.priority >= selectedHandler.priority) {
            selectedHandler = handler;
          }
        });
        busy = true;
        handlers = handlers.filter(handler => handler.id !== selectedHandler.id);
        executeAction(selectedHandler).then(() => busy = false);
      }
    };
    processHandlers();
  });
};
const OVERLAY_BACK_BUTTON_PRIORITY = 100;
const MENU_BACK_BUTTON_PRIORITY = 99; // 1 less than overlay priority since menu is displayed behind overlays

export { MENU_BACK_BUTTON_PRIORITY, OVERLAY_BACK_BUTTON_PRIORITY, blockHardwareBackButton, startHardwareBackButton };