How to call a server side function on Leave event of a ASP.Net TextBox

I am building a user registration form in a开发者_C百科sp.net. I want to check if the username is available or not on the leave event of the TextBox. I am not able to get the Leave Event of the TextBox.

Should I use OnBlur event of the Html TextBox. Please Help.

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How about using TextChanged server-side event and wrapping the whole thing in an UpdatePanel for very quick ajax functionality. If you use this method make sure the AutoPostBack property is set to true for the TextBox control.