Java Script is very popular scripting language tool, because he use small source code, cross platform within many browser and the execution of the script is fast for this, because calculation of the script is made on user's computer and your server will stay available for main applications.

Like in and other developer language and script, while developing in Java Script, developer can dismiss or mess up something and an error wile rise up. This will stop the script or will give a malfunction in web application.

For this we will use some debug tool for catching the errors and to fix them. In this tutorial I will show you How to Debug Java Script with Firebug

Firebug also can debug HTML, CSS sources. Can edit your html in real time, to try different layout with css on the fly, to measure network activity, etc.

Firebug can be called be pressing F12 key, and you have to note that the Firebug have to called after fully page loading. Otherwise he will notify you to reload the webpage.

Here is the sample screenshot from HTML tab in Firebug. You can see that, when select some tag in source code in Firebug, this part of the web page will be selected visually this HTML source code.

Here is the CSS tab in Firebug. In the listed CSS code below you can directly edit your CSS layout and to see the result immediately.

And here is the Firebug debug console where Java Script errors appear. When you click with mouse on the error (green line), your entire Java Script code will be displayed and the problem object, function, declaration, etc will be pointed.