Document Ready на JavaScript

      window.ready = function ready(callback) {
    // in case the document is already rendered
    if (document.readyState !== 'loading') {
        callback();
    }
    // modern browsers
    else if (document.addEventListener) {
        document.addEventListener('DOMContentLoaded', callback);
    }
    // IE <= 8
    else {
        document.attachEvent('onreadystatechange', function(){
            if (document.readyState === 'complete') callback();
        });
    }
};