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JavaScript AJAX Basics (retiring) Programming AJAX Check for the correct ready state

Sharina V. Jones
Sharina V. Jones
11,459 Points
Posted by Sharina V. Jones
Sharina V. Jones
11,459 Points

AJAX Basics: Code Challenge Stage 2

The challenge is

Now that the server has responded with the data, you need to add > it to the page. First select the div with the ID of 'sidebar'. You can >select page elements with IDs like this: >document.getElementById('idName');

This is the code I entered: 

var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
  }
};
xhr.open('GET', 'sidebar.html');
xhr.send();
document.getElementById('sidebar');

I keep getting Bummer! To select the <div> tag with the 'sidebar' ID, you need to pass the ID name as a string to the getElementById method, like this: document.getElementById('sidebar').

Please help!

4 Answers

notf0und
notf0und
11,940 Points

Your document.getElementById('sidebar') is conditional on the "if" statement. Just move that line inside if (xhr.readyState === 4 && xhr.status === 200) { put it here }

Dave McFarland
Dave McFarland
Treehouse Teacher
Dave McFarland
Dave McFarland
Treehouse Teacher

The code has to go inside the conditional statement (and inside the callback function) just like Bryan H points out. This is necessary because AJAX requests are "asynchronous" meaning that the rest of the program and your web page keeps doing its business between when the request is sent and the response returns. Putting document.getElementById('sidebar'); last in the code above, doesn't make it run last. It actually runs BEFORE the server has time to respond to the AJAX request. That's the point of a callback (the function assigend to the onreadystatechange event) to wait until the response comes in -- then and only then should you select the page element.

Michelle Pepe
PLUS
Michelle Pepe
Courses Plus Student 6,125 Points
Michelle Pepe
Michelle Pepe
Courses Plus Student 6,125 Points 
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    document.getElementById('sidebar');
  }
};
xhr.open('GET', 'sidebar.html');
xhr.send();
Dave McFarland
Dave McFarland
Treehouse Teacher
Dave McFarland
Dave McFarland
Treehouse Teacher

Michelle Pepe

To put code into a forum post use triple back ticks -- ``` — around the code. I fixed your code here, but in the future here's a forum discussion that describes how to add HTML, CSS, JavaScript or other code to the forum: https://teamtreehouse.com/forum/posting-code-to-the-forum

Michelle Pepe
Michelle Pepe
Courses Plus Student 6,125 Points

Thank you Dave.

Ary de Oliveira
Ary de Oliveira
28,298 Points
Ary de Oliveira
Ary de Oliveira
28,298 Points

Dry Answer:

Challenge Task 1 of 2

In app.js, we've added an AJAX callback function. You need to complete the request. Add the code to open the AJAX request using the GET method and pointing to the 'footer.html' file:

var request = new XMLHttpRequest(); request.onreadystatechange = function () { if (request.readyState === 4) { document.getElementById("footer").innerHTML = request.responseText; } }; request.open('GET', 'footer.html');