Unable to call Javascript function onload a asp:button using ASP.NET4

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I am unable to call a Javascript function on the OnLoad event of a asp:buttonHTML\[code\]<asp:Button ID="btnFromCalOpen" runat="server" Text=" > " onLoad = "AllHide()" OnClientClick ="ShowCal()" />\[/code\]Javascript\[code\] function AllHide() { alert("Hello"); } \[/code\]Please Help