The RegisterClientScriptBlock method enables you to put a JavaScript function at the top of a page. Thus, the script is in place for the startup of the page in the browser. Its use is illustrated
in the below listing.

<%@ Page Language="C#" %>
<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
string customScript = @"function myalert() { alert(’ASP.NET 101’); }";
Page.ClientScript.RegisterClientScriptBlock(this.GetType(),
"CustomScript", customScript, true);
}
</script>
<script type="text/javascript">
<!--
function myalert() { alert(’ASP.NET 101’); }// -->
</script>
<div>
<input type="submit" name="Button1" value="Button" onclick="myalert();"
id="Button1" />
</div>

From the above listing you can see that you create the JavaScript function myalert() as a string named customScript. Using Page.ClientScript.RegisterClientScriptBlock you then program the script to be placed on the page. The two possible constructions of the RegisterClientScriptBlock method are the following:
- RegisterClientScriptBlock (type, key, script)
- RegisterClientScriptBlock (type, key, script, script tag specification)