Page.ClientScript.RegisterStartupScript doesn't work - why?

Question

i have some code in OnInit hanlder

if (!Page.ClientScript.IsStartupScriptRegistered(GetType(), "MyScript"))
{
    Page.ClientScript.RegisterStartupScript(GetType(), "MyScript", GetStartupScript(), true);
}

here i try to register some java script code. and i want it to work on button click event. but it doesn't execute. it executes only after refreshing page. can anyone explain me why it doesn't execute?

thnx in advance!

Solution

 string msg = "This is variable message";
 Page.ClientScript.RegisterStartupScript(typeof(Page), "well1", "<script>alert('" + msg + "');</script>");