Things that you should be aware of before doing javascript

As you know html is a lenient programming language.you can do mistakes.But anyhow the browser will display the content.But how it will behave is an absurd one.
But when you come into javascript even when you make a small mistake ,you won't even get the undesired output.What I mean by that.It is very difficult to debug your javascript programs.In order to debug your javascript programs you should have exposure about the following addons and opensource software.
https://addons.mozilla.org/en-US/firefox/addon/1843/
https://addons.mozilla.org/en-US/firefox/addon/60/
https://addons.mozilla.org/en-US/firefox/addon/6622/
http://www.aptana.com/
you will be able to realise the features of the above when you started studying javascript.