Whats the '!' for in javascript?

[BIOSTALL]

Hey, i found the following piece of code on the internet:

var newwindow = '';

function popitup(url)
{
if (!newwindow.closed && newwindow.location)
{
newwindow.location.href = url;
}
else
{
newwindow=window.open(url,'name','height=200,width=150');
if (!newwindow.opener) newwindow.opener = self;
}

I was just wondering what the '!' is for in '!newwindow.closed'. I've come across it many times before but never actually understood what it does.

Thanks, BIOSTALL

[Brandoe85]

It's the not operator. Not Operator