i'm a beginner to java script. can anyone help me in this with this.
if iam the user i want to insert a username in the textbox and it check whether it exist (i can do this in php code) or not..if the username exist it focus on the
Can anyone give me an idea.Thanks a lot..
To achieve that, you start from the very bedrock basics. A form submits to a php page, and that php page performs the checks, and updates the page.
Once those basics are in place, you can extract the part that performs the checks to a separate file so that it can be included, and also so that you can send an AJAX request to that same file.
The book [Bulletproof Ajax is the best one for learning how to do what you want to achieve. The web site also provides all of the [url="http://bulletproofajax.com/code/"]code and working examples](http://bulletproofajax.com/) too, of which the Contact Us example from Chapter 6 is a fully working example of the type of technique you wish to use.