I think the previous two posters missed the direction of your question, but on the other side, you didn't provide any useful examples. So my interpretation of your question is as follows :

• You have a website that sends a (HTML) page with some JavaScript code in it that is triggered by an onClick JavaScript event. Said code submits a form on the page back to the server.
  This is easily emulated in Perl, see for example many scripts on this site using LWP::Simple or LWP::UserAgent (search via Super Search).
• Or you have a website that sends some HTML with is then manipulated in the browser with JavaScript and displayed differently based on some decisions made by the JavaScript code.
  This would be much harder or impossible to emulate in Perl, as to emulate JavaScript, you have to write a complete JavaScript emulator in Perl, something which is quite nasty.
• A third possibility could be that you want to remotely control and/or automate your browser. For that purpose, on Windows, have a look at the Internet Explorer automation stuff via Win32::OLE and/or Win32::API, most likely the SendMessage() API (not for the faint of heart though, sending events to other processes can result in interesting behaviour of the whole system)

Maybe these interpretations help you to reformulate your question to match your intentions.

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web
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