JavaScript Timer; JavaScript Duration; Measure the duration of a JavaScript event

function start() {
    startTime = new Date().getTime();
}

function stop() {
    var endTime = new Date().getTime();
    return endTime - startTime;
}

function start() {
    startTime = new Date().getTime();
}

function stop() {
    var endTime = new Date().getTime();
    return endTime - startTime;
}

function doSomething() {
    for (var i = 0; i < 1000000; i++) {
        // Do something
    }
}

<input value="Click me" onclick="start(); doSomething(); alert(stop() + 'ms');" type="button" />