webservices with ajax

Hi All,
I am new to client side functionality of Ajax. I was just going through some online articles and ajax documentation. I knew that we can call code behind code from javascript using ajax. I didn't knew that we have to create a webservice for that. It's easy to write it as a webservice but my point is that is there any limitation of using webservice in that manner. Is there any other way by which we can access code behind methods from javascript?. If yes, then which is the best approach or best practice way.


Thanks,
Nimesh
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