Add JavaScript programmatically using RegisterStartupScript during an Asynchronous postback

You can use below code to call JavaScript from your script page:
ScriptManager.RegisterStartupScript(Me.GetType(), "AlertMe", "alert('test');",False)
btnPostback is control, you can also give "this" for general javgaScript.


Also if you do not have ScriptManager, then you can use below code:

Dim someScript As String = "alertMe"

If (Not ClientScript.IsStartupScriptRegistered(Me.GetType(), someScript)) Then

   ClientScript.RegisterStartupScript(Me.GetType(), someScript, "alert('I was called from Content page!')", True)

End If