How do I execute a JavaScript function on my page load in studio 2008?

How do I execute a JavaScript function on my page load in studio 2008?

 I tried like
body = (System.Web.UI.HtmlControls.HtmlGenericControl)Page.FindControl("body");
body.Attributes.Add("onLoad", "HideButtons();");

But my 'body' variable gets null when I execute the page.

Any idea?

Thanks
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