Detecting an enter key press on an asp.net form (but when using AJAX as well!)

I've been more than familiar with detecting key presses in javascript for quite some time, and used to do it all the time in classic asp, but this time when I came to do it in the .net world, in was a little more involved.

This setup was also the first time I had to cope with Masterpages using AJAX inside them.

So, I have a simple content placeholder, inside this a textbox and these themselves are inside an updatepanel. I also have a modalpopup extender that shows whenever the page causes an update (asyncpostback).

So, to get this to work, I had to tie up my javascript with the ScriptManager.RegisterClientScriptBlock() method and placing the script into a LiteralControl that I had to place on the form also:

if(!Page.IsPostBack)
{
this.textBoxQuery.Attributes.Add("onkeypress", "javascript:return checkEnter(event);");
Page.RegisterHiddenField("__EVENTTARGET", textBoxQuery.ClientID);
string strScript = "function checkEnter(e){ " +
"var characterCode; " +
"if(e && e.which){ " +
"e = e; " +
"characterCode = e.which; " +
"} " +
"else { " +
"e = event; " +
"characterCode = e.keyCode; " +
"} " +
"if (characterCode == 13) " +
"{ " +
" " +
" document.getElementById('" + ButtonSearch.UniqueID + "').click(); " +
" return false; " +
"} " +
"else " +
"{ " +
" return true; " +
"}" +
"}";

ScriptManager.RegisterClientScriptBlock(LitScript, this.GetType(), "regScripts", strScript, true);
}

This now captures the enter key, and handles it as a normal button click event.