2020-04-29 手写AJAX

######完整版

      let url = "";//要请求的url
      let request = new XMLHttpRequest();
      request.open(
        "GET",
        url,
        true
      );
      request.onreadystatechange = function () {
        if (request.readyState === 4 && request.status === 200) {
          console.log(request.responseText);
        }
      };
      request.send();

######精简版

      let url = ""; //要请求的url
      let request = new XMLHttpRequest();
      request.open("GET", url, true);
      request.onload=()=>{console.log(request.responseText)}
      request.send();