freeCodeCamp/curriculum/challenges/chinese/04-data-visualization/json-apis-and-ajax/post-data-with-the-javascript-xmlhttprequest-method.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
587d7faf367417b2b2512be9	使用 XMLHttpRequest 方法发送数据	6	301504	post-data-with-the-javascript-xmlhttprequest-method

--description--

在前面的示例中，你通过外部资源获取数据。 此外，你也可以将数据发送到外部资源，只要该资源支持 AJAX 请求并且你知道 URL。

JavaScript 的XMLHttpRequest方法也用于将数据发布到服务器。 这是一个示例：

const xhr = new XMLHttpRequest();
xhr.open('POST', url, true);
xhr.setRequestHeader('Content-Type', 'application/json; charset=UTF-8');
xhr.onreadystatechange = function () {
  if (xhr.readyState === 4 && xhr.status === 201){
    const serverResponse = JSON.parse(xhr.response);
    document.getElementsByClassName('message')[0].textContent = serverResponse.userName + serverResponse.suffix;
  }
};
const body = JSON.stringify({ userName: userName, suffix: ' loves cats!' });
xhr.send(body);

你之前已经见过这些方法。 Here the open method initializes the request as a POST to the given URL of the external resource, and passes true as the third parameter - indicating to perform the operation asynchronously.

The setRequestHeader method sets the value of an HTTP request header, which contains information about the sender and the request. It must be called after the open method, but before the send method. The two parameters are the name of the header and the value to set as the body of that header.

Next, the onreadystatechange event listener handles a change in the state of the request. A readyState of 4 means the operation is complete, and a status of 201 means it was a successful request. Therefore, the document's HTML can be updated.

Finally, the send method sends the request with the body value. The body consists of a userName and a suffix key.

--instructions--

Update the code so it makes a POST request to the API endpoint. Then type your name in the input field and click Send Message. Your AJAX function should replace Reply from Server will be here. with data from the server. Format the response to display your name appended with the text loves cats.

--hints--

Your code should create a new XMLHttpRequest.

assert(code.match(/new\s+?XMLHttpRequest\(\s*?\)/g));

Your code should use the open method to initialize a POST request to the server.

assert(code.match(/\.open\(\s*?('|")POST\1\s*?,\s*?url\s*?,\s*?true\s*?\)/g));

Your code should use the setRequestHeader method.

assert(
  code.match(
    /\.setRequestHeader\(\s*?('|")Content-Type\1\s*?,\s*?('|")application\/json;\s*charset=UTF-8\2\s*?\)/g
  )
);

Your code should have an onreadystatechange event handler set to a function.

assert(code.match(/\.onreadystatechange\s*?=/g));

Your code should get the element with class message and change its textContent to userName loves cats

assert(
  code.match(
    /document\.getElementsByClassName\(\s*?('|")message\1\s*?\)\[0\]\.textContent\s*?=\s*?.+?\.userName\s*?\+\s*?.+?\.suffix/g
  )
);

Your code should use the send method.

assert(code.match(/\.send\(\s*?body\s*?\)/g));

--seed--

--seed-contents--

<script>
  document.addEventListener('DOMContentLoaded', function(){
    document.getElementById('sendMessage').onclick = function(){

      const userName = document.getElementById('name').value;
      const url = 'https://jsonplaceholder.typicode.com/posts';
      // Add your code below this line


      // Add your code above this line
    };
  });
</script>

<style>
  body {
    text-align: center;
    font-family: "Helvetica", sans-serif;
  }
  h1 {
    font-size: 2em;
    font-weight: bold;
  }
  .box {
    border-radius: 5px;
    background-color: #eee;
    padding: 20px 5px;
  }
  button {
    color: white;
    background-color: #4791d0;
    border-radius: 5px;
    border: 1px solid #4791d0;
    padding: 5px 10px 8px 10px;
  }
  button:hover {
    background-color: #0F5897;
    border: 1px solid #0F5897;
  }
</style>

<h1>Cat Friends</h1>
<p class="message box">
  Reply from Server will be here
</p>
<p>
  <label for="name">Your name:
    <input type="text" id="name"/>
  </label>
  <button id="sendMessage">
    Send Message
  </button>
</p>

--solutions--

<script>
  document.addEventListener('DOMContentLoaded', function(){
    document.getElementById('sendMessage').onclick = function(){

      const userName = document.getElementById('name').value;
      const url = 'https://jsonplaceholder.typicode.com/posts';
      // Add your code below this line
      const xhr = new XMLHttpRequest();
      xhr.open('POST', url, true);
      xhr.setRequestHeader('Content-Type', 'application/json; charset=UTF-8');
      xhr.onreadystatechange = function () {
        if (xhr.readyState === 4 && xhr.status === 201){
          const serverResponse = JSON.parse(xhr.response);
          document.getElementsByClassName('message')[0].textContent = serverResponse.userName + serverResponse.suffix;
       }
     };
     const body = JSON.stringify({ userName: userName, suffix: ' loves cats!' });
     xhr.send(body);
      // Add your code above this line
    };
  });
</script>

<style>
  body {
    text-align: center;
    font-family: "Helvetica", sans-serif;
  }
  h1 {
    font-size: 2em;
    font-weight: bold;
  }
  .box {
    border-radius: 5px;
    background-color: #eee;
    padding: 20px 5px;
  }
  button {
    color: white;
    background-color: #4791d0;
    border-radius: 5px;
    border: 1px solid #4791d0;
    padding: 5px 10px 8px 10px;
  }
  button:hover {
    background-color: #0F5897;
    border: 1px solid #0F5897;
  }
</style>

<h1>Cat Friends</h1>
<p class="message">
  Reply from Server will be here
</p>
<p>
  <label for="name">Your name:
    <input type="text" id="name"/>
  </label>
  <button id="sendMessage">
    Send Message
  </button>
</p>