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JavaScript AJAX Basics Programming AJAX Check for the correct ready state

Posted by trottly
trottly
5,394 Points

Using `querySelector('#sidebar')` instead of `getElementById('sidebar')

The challenge task 3 of 4 is forcing me to use the getElementById('sidebar') document method to select the div in question.

app.js 
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
  if ( xhr.readyState === 4) { 
    // Server has sent back complete response.  
    if ( xhr.status === 200) { 
      // Server return status is okay (200).  
      // Add data to page.  
      sidebar = document.querySelector('#sidebar');  
    } 
  }
};
xhr.open('GET', 'sidebar.html');
xhr.send();
index.html 
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>AJAX with JavaScript</title>
  <script src="app.js"></script>
</head>
<body>
  <div id="main">
    <h1>AJAX!</h1>
  </div>
  <div id="sidebar"></div>
</body>
</html>

1 Answer

Peter Vann
Peter Vann
36,425 Points

HI!

In the real world, document.querySelector('#sidebar) should work just fine.

Sometimes the task test programs are not very flexible though...

This passes all four tasks:

var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
  if ( xhr.readyState === 4) { 
    // Server has sent back complete response.  
    if ( xhr.status === 200) { 
      // Server return status is okay (200).  
      // Add data to page.  
     document.getElementById('sidebar').innerHTML = xhr.responseText;
    } 
  }
};
xhr.open('GET', 'sidebar.html');
xhr.send();

It's NOT part of the challenge, but I have recently learned that innerHTML can lead to serious XSS vulnerabilities (so in the real world use it cautiously).

More info:

https://gomakethings.com/preventing-cross-site-scripting-attacks-when-using-innerhtml-in-vanilla-javascript/

https://medium.com/front-end-weekly/javascript-innerhtml-innertext-and-textcontent-b75ec895cbe3

https://teamtreehouse.com/library/owasp-top-10-vulnerabilities

I hope that helps.

Stay safe and happy coding!