JavaScript global variable trouble

I'm having trouble with global variabl开发者_如何转开发es in JavaScript. From every article I've read a variable declared out of a function has a complete scope. But below alert(leftMargin); results in 'undefined' when inside a function;

var leftMargin = 36;
alert(leftMargin); /* '36' */

function position(direction) {
    alert(leftMargin); /* 'undefined' */
}

Are you positive it's undefined?

<script type="text/javascript">
    var leftMargin = 36;
    alert(leftMargin); /* '36' */
    function position(direction) {
        alert(leftMargin); /* '36' */
    }
    position();
</script>

It alerts 36 twice for me, as expected. It might be unset between defining the leftMargin variable and actually calling position().