XMLHttpRequest: readystatechange 事件

addEventListener("readystatechange", (event) => {});

onreadystatechange = (event) => {};

const xhr = new XMLHttpRequest();
const method = "GET";
const url = "https://mdn.org.cn/";

xhr.open(method, url, true);
xhr.onreadystatechange = () => {
  // In local files, status is 0 upon success in Mozilla Firefox
  if (xhr.readyState === XMLHttpRequest.DONE) {
    const status = xhr.status;
    if (status === 0 || (status >= 200 && status < 400)) {
      // The request has been completed successfully
      console.log(xhr.responseText);
    } else {
      // Oh no! There has been an error with the request!
    }
  }
};
xhr.send();