再次运行脚本后提示aint工作

Question

我第一次运行此脚本时，提示工作， 但是第二次正在运行我收到此错误：

install.js：27未捕获的TypeError：无法读取null的属性“提示” 在HTMLButtonElement.installPWA（install.js：27） 有人知道修复吗

let deferredInstallPrompt = null;
const installButton = document.getElementById('boutonInstall');
installButton.addEventListener('click', installPWA);

// Add event listener for beforeinstallprompt event
window.addEventListener('beforeinstallprompt', saveBeforeInstallPromptEvent);

/**
 * Event handler for beforeinstallprompt event.
 *   Saves the event & shows install button.
 *
 * @param {Event} evt
 */
function saveBeforeInstallPromptEvent(evt) {
  // CODELAB: Add code to save event & show the install button.
  deferredInstallPrompt = evt;
  installButton.removeAttribute('hidden');
  //AJOUT de SHany
  showInstallPromotion();
}

function installPWA(evt) {
  // Add code show install prompt & hide the install button.
  deferredInstallPrompt.prompt();
  // Hide the install button, it can't be called twice.
  evt.srcElement.setAttribute('hidden', true);

  // Log user response to prompt.
  deferredInstallPrompt.userChoice.then((choice) => {
    if (choice.outcome === 'accepted') {
      console.log('User accepted the A2HS prompt', choice);
    } else {
      console.log('User dismissed the A2HS prompt', choice);
    }
    deferredInstallPrompt = null;
  });
}

// Add event listener for appinstalled event
window.addEventListener('appinstalled', logAppInstalled);
/**
 * Event handler for appinstalled event.
 *   Log the installation to analytics or save the event somehow.
 *
 * @param {Event} evt
 */
function logAppInstalled(evt) {
  // Add code to log the event
  console.log('Hello World was installed.', evt);
}