Why is ASP.NET adding JS to get the Form element?

I am removing the following from my aspx files:

<script type="text/javascript">
    //<![CDATA[
    var theForm = document.forms['aspnetForm'];
    if (!theForm) {
        theForm = document.aspnetForm;
    }
    function __doPostBack(eventTarget, eventArgument) {
        if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
            theForm.__EVENTTARGET.value = ev开发者_运维问答entTarget;
            theForm.__EVENTARGUMENT.value = eventArgument;
            theForm.submit();
        }
    }
    //]]>
</script>   

But when I run the application, it's added back in. How and why is this? How can I permanently remove it?

asp.net uses the _doPostBack JavaScript code to handle control post back logic, further info can be found in this article - http://aspalliance.com/895_Understanding_the_JavaScript___doPostBack_Function.all

It's Javascript that is automatically generated by ASP.NET to support some of the controls that require certain postback logic, such as asp:LinkButton and asp:ImageButton. These aren't standard HTML Form controls, so they require Javascript to trigger a POST when clicked on in the browser.

The script should only actually be generated if ASP.NET thinks you need it, so perhaps you're using a control that does? It shouldn't generate it otherwise. For instance, a plain ASPX page with only a asp:Button control won't generate the script, but if you add an asp:LinkButton, it will.