Found a great plug – Firebug in for Firefox which is of great use to Javascript /Ajax developers.
Here are the features I like
1. Detects errors in HTML and the error messages are useful
2. Dynamically added HTML is shown too. – This feature is really a godsend for AJAX developers who more often than not, have to modify HTML using DOM. (For e.g. dynamically adding rows to an HTML table etc). Javascript debugging for such cases was very difficult because the normal ‘View Source’ does not show the newly added code and usually developers had to fill in alerts to identify the problem. But Firebug changes all that and we can see the dynamically changed HTML
3. Inspect mode – Pointing the mouse over the page highlights the code associated with that place and you can even modify the code.
The above 3 are the features I found most useful.
Others good features include
1. View DOM structure of an HTML
2. Measure Network activity – This is great to have if you make AJAX calls and you need to measure the response time.
This plug in has saved me hours trying to debug Javascript code and I recommend this as a godsend to all Web Developers.
UPDATE: Internet Explorer too has a plugin for Javascript debugging. Not as feature some as Firebug but useful nonetheless. Get the plugin for IE here
Hello World 