How to call javascript function and code behind using button

[babbsack]

How to call javascript function and code behind function using button?\[code\]<asp:button id="btnSave" onclick="btnSave();" onclientclick ="return javascriptfunction();" runat="server"></asp:button>\[/code\]I tried like this too. but no response.\[code\]<asp:button id="btnSave" onclick="btnSave();" onclientclick ="return true;" runat="server"></asp:button>\[/code\]even, javascript function return true, its not calling codebehind function. May i know reason?