Scripting can't call javascript function before submit form

[wwtaotao]

I want to test my application by script, I wrote a script to login as below:

// load the account name and password
loadVariables accounts.txt

// bring up the login screen
setDOMElement name=user_id
navigate http://w3x32s05-pv010.pd.local

// log in
sleep 5
setValue name=user_id %ADMINISTRATOR%
setValue name=password %PASSWORD%
setDOMElement innerText=My Institution
sleep 5
submitForm name=login

It runs well but just couldn't login successfully.
After I debug code, I found the root reason is because the submitForm action won't run validate_form javascript funciton in my login page before submit(it will call the function if we submit it by manual).
my form is like this:
<form onsubmit="return validate_form( this, true );" method="POST" action="http://w3x32s05-pv010/webapps/login/" NAME="login" >
the validate_form javascript will encode the password by a token value, it means the encode password will change each time, I can't set the encode password value too.
Does it has any way I can write the script to login in my application? thanks.