So what you want is a field where a user can type in a name and it returns a message stating if it is taken or not? If so you will need to use ajax and a server language such as PHP. The javascript can send to and receive from the script, but the server script will have to do the actual checking.

Javascript is 100% run from the users browser and should never under any circumstances be used to access a secured database.

This might help (found from google search ajax validate if username is taken) http://jqueryfordesigners.com/using-...alidate-forms/

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