javascript error: submit form using javascript with html:button for different action

[752004]

in html:button onclick method I am calling a javascript function where
my code is
document.forms[1].action="...";
document.forms[1].submit();

I have used html:form where I mentioned the action which is different that script action...

It gives javascript error on this line document.forms[1].action="..."; saying that object or method not supported