Execute JavaScript function from ASP.NET codebehind From S uprotim Agarwal blog. Calling a JavaScript function from codebehind is quiet simple, yet it confuses a lot of developers. Here's how to do it. Declare a JavaScript function in your code as shown below: JavaScript < head runat ="server"> < title > Call JavaScript From CodeBehind </ title > < script type ="text/javascript"> function alertMe() { alert( 'Hello' ); } </ script > </ head > In order to call it from code behind, use the following code in your Page_Load C# protected void Page_Load( object sender, EventArgs e) { if (!ClientScript.IsStartupScriptRegistered( "alert" )) { Page.ClientScript.RegisterStartupScript( this .GetType(), "alert" , "alertMe();" , true ); } } VB.NET If (Not ClientScript.IsStartupScriptRegistered( "alert&q