Untitled

<!doctype html>
<html lang="en">
<head>
	<meta charset="utf-8">
	<title>Test Date#setHours</title>
</head>
<body>
	<div>
		<div id="user-agent"></div>
		<div id="results"></div>
	</div>
	<script type="text/javascript">
	var userAgent = document.getElementById('user-agent');
	var results = document.getElementById('results');

	userAgent.innerHTML = window.navigator.userAgent;
	window.addEventListener('load', function(event) {
		var perf = typeof performance != 'undefined' ? performance : Date;
		var iterations = 2000000;
		setTimeout(() => {
			var test0 = Promise.resolve(new Date()).then(dt => {
				var start = perf.now();

				for (var i = 0; i < iterations; ++i) {
					dt.setHours(i % 24);
				}

				return perf.now() - start;
			});
			var test1 = Promise.resolve(new Date()).then(dt => {
				var start = perf.now();

				for (var i = 0; i < iterations; ++i) {
					dt.setHours(i % 24, 0, 0, 0);
				}

				return perf.now() - start;
			});
			var test2 = Promise.resolve(new Date()).then(dt => {
				var start = perf.now();

				for (var i = 0; i < iterations; ++i) {
					dt.setHours(i % 24, 0, 0, 0);
					dt.setHours(0);
				}

				return perf.now() - start;
			});

			// yes, these are CPU-bound performance tests, using promise to seperate them into different IO passes.
			Promise.all([test0, test1, test2]).then(times => {
				results.innerHTML = `
					<p>Each of the following was for <code>${iterations}</code> iterations.</p>
					<dl>
						<dt>Set only hour</dt>
						<dd><code>${times[0].toFixed(4)}</code></dd>
						<dt>Set hour, minute, second, millisecond</dt>
						<dd><code>${times[1].toFixed(4)}</code></dd>
						<dt>Do both</dt>
						<dd><code>${times[2].toFixed(4)}</code></dd>
					</dl>
				`;
			});
		}, 10);
	});
	</script>
</body>
</html>