如何等待身体的孩子？

Question

在此页面上，我希望我的 Chrome 扩展程序等待所有页面元素完全加载。我怎么做？第一个

MutationObserver

有效，第二个无效。

var waitForBody = function() {
  return new Promise(resolve => {
    if (document.documentElement.getElementsByTagName('body')) {
      return resolve(document.documentElement.getElementsByTagName('body'));
    }
    const observer = new MutationObserver(mutations => {
      if (document.documentElement.getElementsByTagName('body')) {
        resolve(document.documentElement.getElementsByTagName('body'));
        observer.disconnect();
      }
    });
    observer.observe(document.documentElement);
  });
}

var waitById = function(elmId) {
  return new Promise(resolve => {
    if (document.getElementById(elmId)) {
      return resolve(document.getElementById(elmId));
    }
    const observer = new MutationObserver(mutations => {
      if (document.getElementById(elmId)) {
        resolve(document.getElementById(elmId));
        observer.disconnect();
      }
    });
    observer.observe(document.body, {childList: true});
  });
}

waitForBody().then((elm) => {
    console.log('elm is ready');
    console.log(document.getElementById('#xt-popover'));
  waitById('#xt-popover').then((elm2) => {
    console.log('elm2 is ready');
  });
});

# elm is ready
# null