Javascript 检查http响应代码以显示相应的故障消息

我有一个javascript函数，它获取表单数据并通过http post请求将其发送到服务器。我现在需要检查返回的状态代码是否为201，否则显示错误消息：

function load(){

console.log(document);
var form = document.getElementById("myform");

form.onsubmit = function (e) {
  // stop the regular form submission
  e.preventDefault();

  // collect the form data while iterating over the inputs
  var data = {};
  for (var i = 0, ii = form.length; i < ii; ++i) {
    var input = form[i];
    if (input.name) {
      data[input.name] = input.value;
    }
  }

  // construct an HTTP request
  var xhr = new XMLHttpRequest();
  xhr.open(form.method, form.action, true);
  xhr.setRequestHeader('Content-Type', 'application/json; charset=UTF-8');

  // send the collected data as JSON
  xhr.send(JSON.stringify(data));

  xhr.onloadend = function () {
    // done
  };
};
}

---

这通常只是

状态

var xhr = new XMLHttpRequest();

xhr.open(form.method, form.action, true);
xhr.setRequestHeader('Content-Type', 'application/json; charset=UTF-8');
xhr.send(JSON.stringify(data));

xhr.onreadystatechange = function()
    if (xhr.readyState == 4 && xhr.status == 201) {
    //        ^^ request complete      ^^ and returned status was 201
    }
}

---

谢谢，我想这正是我想要的！如果我在后面添加一个else If语句来表示If xhr.status！=201，我如何让浏览器显示代码和错误消息？就像您显示任何其他内容一样，在这种情况下，执行类似于

element.innerHTML='error-201'

var xhr = new XMLHttpRequest();

xhr.open(form.method, form.action, true);
xhr.setRequestHeader('Content-Type', 'application/json; charset=UTF-8');
xhr.send(JSON.stringify(data));

xhr.onreadystatechange = function()
    if (xhr.readyState == 4 && xhr.status == 201) {
    //        ^^ request complete      ^^ and returned status was 201
    }
}