List all CSS classes in a HTML document to the console.

class-list.html

<script type="text/javascript">
var used = [];
var elements = null;

//get all elements
if (typeof document.getElementsByTagName != 'undefined') {
    elements = document.getElementsByTagName('*');
}

if (!elements || !elements.length) {
    elements = document.all; // ie5
}

//loop over all element
for (var i = 0; i < elements.length; i++){

    //loop over element's classes
    var classes = elements[i].className.split(' ');
    for (var j = 0; j < classes.length; j++) {

        var name = classes[j];

        //add if not exists
        if (name.length > 0 && used.indexOf(name) === -1) {
            used.push(name);
        }
    }
}

console.log(used.join(' '));

</script>