The AJAX Errors That No-one Else Talks About

Handling AJAX errors is about more than just checking the readyState, status and statusText.

The W3 working draft for the XMLHttpRequest object states that when the readyState of an XMLHttpRequest is 3 or 4, then status and statusText must be available. These values can then be used to determine if the request was successful or not. By and large this is true, you will see a status of 200 when everything is OK and something like 404 when you make a mistake. What isn't specified however is what happens if the network connection goes down while the XMLHttpRequest is in flight or is down when the XMLHttpRequest is sent.

The following table details the values obtained or the behaviour observed in various browsers when an XMLHttpRequest fails due to a network failure.

Obviously this list is very far from complete. If you know the behaviour of other browsers or other browser versions, please let me know (via the comment section below) and I'll update the list accordingly. To run the test yourself, you can use the Event Driven AJAX Demonstration and

1. Turn debugging on
2. Click "Lighten Page"
3. You should see "getEvents waiting.." in the debug window
4. Sever your network connection (or if you are running the demo locally, terminate the web server)
5. record the "readyState", "status" and "statusText" reported in the debug window.

To create your own test:

1. Create a page that sends and AJAX request when a user clicks a link or button
2. Load the page
3. Sever your network connection (or if you are running the test locally, terminate the web server)
4. Click on the link or button to send the request
5. record the values of "readyState", "status" and "statusText" or record if an exception is thrown trying to access the values.

Admittedly, XMLHttpRequests rarely fail due to network issues, but it is nice to be able to detect when this occurs and handle it gracefully with your client side code. Probably the safest way to handle this type of error is to display a message in an appropriate place on your page. If your error message widget uses images you should try to pre-load these when the page loads (if possible), because the chances are that if the XMLHttpRequest failed, then an image request will fail too. For the same reason you should avoid redirecting the user to another page, because the chances are they won't be able to reach that either.

Technorati : AJAX, AJAX Error Handling, Error Handling

 Print This Post

If you like this article, then let other know: These icons link to social bookmarking sites where readers can share and discover new web pages.

• 
• 
• 
• 
• 
• 
• 
• 
• 
• 

Tags: AJAX, Error, network

4 comments.

Vistered Little Theme »« (Re)Introducing Javascript And Hidden Applets (JAHA)