Firebug Tip - When Ajax Calls Go Bad...

Soon to be a new Fox special - this is something that’s been bugging me for quite some time. I use Firebug every single day, but I’ve noticed that it doesn’t really keep a history of events. Why do I need a history? I’ve noticed that in some situations, if my code does an Ajax call to foo.cfm, and foo.cfm throws a ColdFusion exception, then the browser may go to a new page. So for example, imagine this link: <a href="" onclick="doFoo();return false">Do It</a>

Normally this works fine, but if doFoo screws up, the browser ‘misses’ the return false and can send you to a new page. This makes debugging difficult sometimes. So for example, if doFoo did an Ajax request, I’d actually see the red response in Firebug for a split second before the browser went to the new URL. Firebug would then lose the data as it’s in a new request.

The browser error console keeps a history, but what I really need is the response from the Ajax call in Firebug. If I have that, I can look at what ColdFusion returned and see the error.

Ok, so it turns out there is a way to deal with this. If you open up Firebug, click on Script, and then go to Options, there is a “Break on All Errors” option. It took me a while to find this because there are multiple options link on the page. I’ve made it obvious here:

Once you activate this, any error will cause the browser to stop. You can then click on the Net tab to examine the XHR request and see the response.

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Raymond is a developer advocate. He focuses on JavaScript, serverless and enterprise cat demos. If you like this article, please consider visiting my Amazon Wishlist or donating via PayPal to show your support. You can even buy me a coffee!

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