116 lines
4.9 KiB
Markdown
116 lines
4.9 KiB
Markdown
---
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id: 587d7faf367417b2b2512be9
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title: Post Data with the JavaScript XMLHttpRequest Method
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challengeType: 6
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---
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## Description
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<section id='description'>
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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.
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JavaScript's <code>XMLHttpRequest</code> method is also used to post data to a server. Here's an example:
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<blockquote>req=new XMLHttpRequest();<br>req.open("POST",url,true);<br>req.setRequestHeader('Content-Type','text/plain');<br>req.onreadystatechange=function(){<br> if(req.readyState==4 && req.status==200){<br> document.getElementsByClassName('message')[0].innerHTML=req.responseText;<br> }<br>};<br>req.send(userName);</blockquote>
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You've seen several of these methods before. Here the <code>open</code> method initializes the request as a "POST" to the given URL of the external resource, and uses the <code>true</code> Boolean to make it asynchronous.
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The <code>setRequestHeader</code> method sets the value of an HTTP request header, which contains information about the sender and the request. It must be called after the <code>open</code> method, but before the <code>send</code> method. The two parameters are the name of the header and the value to set as the body of that header.
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Next, the <code>onreadystatechange</code> event listener handles a change in the state of the request. A <code>readyState</code> of 4 means the operation is complete, and a <code>status</code> of 200 means it was a successful request. The document's HTML can be updated.
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Finally, the <code>send</code> method sends the request with the <code>userName</code> value, which was given by the user in the <code>input</code> field.
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</section>
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## Instructions
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<section id='instructions'>
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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".
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: Your code should create a new <code>XMLHttpRequest</code>.
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testString: assert(code.match(/new\s+?XMLHttpRequest\(\s*?\)/g), 'Your code should create a new <code>XMLHttpRequest</code>.');
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- text: Your code should use the <code>open</code> method to initialize a "POST" request to the server.
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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.');
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- text: Your code should use the <code>setRequestHeader</code> method.
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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.');
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- text: Your code should have an <code>onreadystatechange</code> event handler set to a function.
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testString: assert(code.match(/\.onreadystatechange\s*?=/g), 'Your code should have an <code>onreadystatechange</code> event handler set to a function.');
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- text: Your code should get the element with class <code>message</code> and change its inner HTML to the <code>responseText</code>.
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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>.');
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- text: Your code should use the <code>send</code> method.
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testString: assert(code.match(/\.send\(\s*?userName\s*?\)/g), 'Your code should use the <code>send</code> method.');
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='html-seed'>
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```html
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<script>
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document.addEventListener('DOMContentLoaded',function(){
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document.getElementById('sendMessage').onclick=function(){
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var userName=document.getElementById('name').value;
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// Add your code below this line
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// Add your code above this line
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};
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});
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</script>
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<style>
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body {
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text-align: center;
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font-family: "Helvetica", sans-serif;
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}
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h1 {
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font-size: 2em;
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font-weight: bold;
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}
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.box {
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border-radius: 5px;
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background-color: #eee;
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padding: 20px 5px;
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}
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button {
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color: white;
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background-color: #4791d0;
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border-radius: 5px;
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border: 1px solid #4791d0;
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padding: 5px 10px 8px 10px;
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}
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button:hover {
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background-color: #0F5897;
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border: 1px solid #0F5897;
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}
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</style>
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<h1>Cat Friends</h1>
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<p class="message box">
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Reply from Server will be here
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</p>
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<p>
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<label for="name">Your name:
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<input type="text" id="name"/>
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</label>
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<button id="sendMessage">
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Send Message
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</button>
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</p>
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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// solution required
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```
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</section>
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