To fake the javascript, you read it , and figure out what it does. Then do those actions in perl (or ignore them if you don't care.) In this case it might look like code that follows , but it all depends on what the javascript does.

   $agent->submit_form(
        form_name => 'hidden_form',
        fields    => { 'newfield1' => 'val1', 'newfield2' => 'val2' },
     );
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This is what the javascript looks like, how do you think I can fake it.

function __doPostBack(eventTarget, eventArgument) {
    var theform = document.Home;
        theform.__EVENTTARGET.value = eventTarget;
        theform.__EVENTARGUMENT.value = eventArgument;
        theform.submit();
    }
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