Help with JavaScript and html forms.

I need help getting data from a form input into the url of a popup window.

This is what I've tried:

<form name="form" action="post.php" method="post">
Your name:<br>
<input type="text" name="name">
<input type="submit" name="submit" value="Submit" onClick="window.open('http://www.website.com/site.php?name= + form.name.value','newwindow','width=500','height=500');>
</form>

Code (markup):

Why isn't this working and what can I do to make it work?

 

change

form.name.value

to

document.form.name.value