js event on page loading

js event on page loading.txt

    <script>
        var eventHandler =function (event) {
            console.log('Event: ' + event.type);
//            console.log(event.timeStamp);
            console.log('Document state: '+document.readyState);

            var end = new Date().getTime();
            var time = end - start;
            console.log('Execution time: ' + time);
            console.log('\n');
        };

        var start = new Date().getTime();
        console.log(document.readyState);

        document.addEventListener('readystatechange', eventHandler, false);
        document.addEventListener('DOMContentLoaded', eventHandler, false);
        window.addEventListener('load', eventHandler, false);
    </script>