From mediacollege.com:
"The following example shows a text field in a form:
<form name="myform">
<input type="text" name="mytextfield">
</form>
Add the following code to the body tag, substituting the form and field names for your own:
<body OnLoad="document.myform.mytextfield.focus();">
That's all there is to it — the OnLoad command instructs the browser to wait until all elements are loaded and then set the focus to the specified form/text field."
Since the on_load_xxx.js content will be put between the quotes in the Zen Cart <body> tag, it looks like its content could be
Code:
document.quick_find.keyword.focus()