how to show alert message

how to show alert message

Response.Write("<script language='javascript'>alert('Your Message!')</script>");

OR

string script = "<script language='javascript'>alert('Your Message!');</script>";
ClientScript.RegisterStartupScript(typeof(Page), "Message", script);

OR

Call function when page is load

Page.RegisterStartupScript("onload", "<script language='javascript' type='text/javascript'>functionname();</script>");

OR

<script language='javascript' type='text/javascript'>
function ShowAlert() {
alert('Your Message!');
return false;
}
</script>

<a href="#" onclick="javascript:ShowAlert();">ShowAlert</a>