does asp.net validation controls envoke any javascript event ?

Hi, all
My application has a left side bar (a div) and main div.
To make side bar's height stretch as main div does, I use following javascript .
<script language="javascript" type="text/javascript">
   
    var divSideBar = document.getElementById('ctl00_ctl00_ContentPlaceHolder1_divSideBar')
    if (divSideBar) {
        divSideBar.style.height = document.getElementById("divMainContent").clientHeight + 20+"px";  
    }
  
</script>
This works fine until I added validation to my page.
when validation fails, the error text appears and they make the height of main div bigger, and I need to call that javascript again to make sidebar stretch.
My question is, are there any specific javascript event I can call my javascript fun ...