Setting javascript variable to false?

[Jeffry Killen <jekillen@xxxxxxxxxxx>]

Hello;

I have javascript global variable in a page that is supposed to be
initialized by php:

// $dual is boolean true/false

var dual = <?php print $dual ?>

But what happens when the page loads is:

var dual = ; // true/false is not written to the page. javascript syntax checker complains.

How would I output a string version of true/false that
javascript will see as a boolean value?

I had been sending $dual as 'true'/'false'

but then when checking dual:
if(dual)
  {
   // if dual is the string 'false', the test passes.
}

Thank you for time and attention
JK