e.timeStamp vs Date.now()

event_timestamp.js

var t1, t2;

function sleep(ms) {
    var s = Date.now();
    while (Date.now() - s < ms);
}

document.addEventListener('mousemove', function(e) {
    if (!t1) {
        t1 = Date.now();
        t2 = e.timeStamp;
        return;
    }
    console.log(
        'time:', Date.now() - t1,
        'ts:', e.timeStamp - t2,
        'x:', e.clientX, 'y:', e.clientY
    );
    sleep(1000);
});