如何修复document.body是null-error

window.onload = function() {
  console.log(document.body);
}

document.addEventListener("DOMContentLoaded", function() {
  console.log(document.body);
});

const script = document.currentScript || (() => {
  const scripts = document.getElementsByTagName('script');
  return scripts[scripts.length - 1];
})();
console.log(script);

// 在主线程中
const worker = new Worker('worker.js');
worker.onmessage = function(event) {
  console.log(event.data);
};

// 在 worker.js 中
self.onmessage = function(event) {
  const message = 'Hello, main thread!';
  self.postMessage(message);
};