freeCodeCamp/curriculum/challenges/04-data-visualization/json-apis-and-ajax/Post Data with the JavaScript XMLHttpRequest Method.md

id, title, challengeType

id	title	challengeType
587d7faf367417b2b2512be9	Post Data with the JavaScript XMLHttpRequest Method	6

Description

In the previous examples, you received data from an external resource. You can also send data to an external resource, as long as that resource supports AJAX requests and you know the URL. JavaScript's XMLHttpRequest method is also used to post data to a server. Here's an example:

req=new XMLHttpRequest();
req.open("POST",url,true);
req.setRequestHeader('Content-Type','text/plain');
req.onreadystatechange=function(){
  if(req.readyState==4 && req.status==200){
    document.getElementsByClassName('message')[0].innerHTML=req.responseText;
  }
};
req.send(userName);

You've seen several of these methods before. Here the open method initializes the request as a "POST" to the given URL of the external resource, and uses the true Boolean to make it asynchronous. 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 200 means it was a successful request. The document's HTML can be updated. Finally, the send method sends the request with the userName value, which was given by the user in the input field.

Instructions

Update the code to create and send a "POST" request. Then enter your name in input box and click "Send Message". Your AJAX function will replace "Reply from Server will be here." with the reply of the server. In this case, it is your name appended with " loves cats".

Tests

- text: Your code should create a new <code>XMLHttpRequest</code>.
  testString: 'assert(code.match(/new\s+?XMLHttpRequest\(\s*?\)/g), "Your code should create a new <code>XMLHttpRequest</code>.");'
- text: Your code should use the <code>open</code> method to initialize a "POST" request to the server.
  testString: 'assert(code.match(/\.open\(\s*?("|")POST\1\s*?,\s*?url\s*?,\s*?true\s*?\)/g), "Your code should use the <code>open</code> method to initialize a "POST" request to the server.");'
- text: Your code should use the <code>setRequestHeader</code> method.
  testString: 'assert(code.match(/\.setRequestHeader\(\s*?("|")Content-Type\1\s*?,\s*?("|")text\/plain\2\s*?\)/g), "Your code should use the <code>setRequestHeader</code> method.");'
- text: Your code should have an <code>onreadystatechange</code> event handler set to a function.
  testString: 'assert(code.match(/\.onreadystatechange\s*?=/g), "Your code should have an <code>onreadystatechange</code> event handler set to a function.");'
- text: Your code should get the element with class <code>message</code> and change its inner HTML to the <code>responseText</code>.
  testString: 'assert(code.match(/document\.getElementsByClassName\(\s*?("|")message\1\s*?\)\[0\]\.innerHTML\s*?=\s*?.+?\.responseText/g), "Your code should get the element with class <code>message</code> and change its inner HTML to the <code>responseText</code>.");'
- text: Your code should use the <code>send</code> method.
  testString: 'assert(code.match(/\.send\(\s*?userName\s*?\)/g), "Your code should use the <code>send</code> method.");'

Challenge Seed

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

      var userName=document.getElementById('name').value;
      // 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>

Solution

// solution required