Detecting browser print event

You can now detect a print request in IE 5+, Firefox 6+, Chrome 9+, and Safari 5+ using the following technique:

(function() {
    var beforePrint = function() {
        console.log('Functionality to run before printing.');
    };
    var afterPrint = function() {
        console.log('Functionality to run after printing');
    };

    if (window.matchMedia) {
        var mediaQueryList = window.matchMedia('print');
        mediaQueryList.addListener(function(mql) {
            if (mql.matches) {
                beforePrint();
            } else {
                afterPrint();
            }
        });
    }

    window.onbeforeprint = beforePrint;
    window.onafterprint = afterPrint;
}());

I go into more detail into what this is doing and what it can be used for at http://tjvantoll.com/2012/06/15/detecting-print-requests-with-javascript/.