denilsonsa/index.html

## index.html
<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8"/>
	<title>getElementsByClassName vs getElementById vs querySelector</title>
	<script src="https://cdnjs.cloudflare.com/ajax/libs/benchmark/1.0.0/benchmark.min.js"></script>
	<script src="./suite.js"></script>
</head>
<body>
	<h1>Open the console to view the results</h1>
	<h2><code>cmd + alt + j</code> or <code>ctrl + alt + j</code></h2>
</body>
</html>

## suite.js
"use strict";

(function (factory) {
	if (typeof Benchmark !== "undefined") {
		factory(Benchmark);
	} else {
		factory(require("benchmark"));
	}
})(function (Benchmark) {
	var suite = new Benchmark.Suite;

	Benchmark.prototype.setup = function () {
		window.generated_divs = 5000;

		let root = document.createElement("div");

		for(let i = 0; i < generated_divs; i++) {
		    let el = document.createElement("div");
		    el.id = `foo${i}`;
		    el.className = `foo${i}`;
		    el.setAttribute(`foo${i}`, '');
		    root.appendChild(el);
		}

		document.body.appendChild(root);
	};

	Benchmark.prototype.teardown = function () {
		document.body.removeChild(root);
		root = null;
	};

	suite.add("getElementById", function () {
		// getElementById
		let i = Math.floor(Math.random() * window.generated_divs);
		let element = document.getElementById(`foo${i}`);
	});

	suite.add("getElementsByClassName", function () {
		// getElementsByClassName
		let i = Math.floor(Math.random() * window.generated_divs);
		let element = document.getElementsByClassName(`foo${i}`);
	});

	suite.add("querySelector('#id')", function () {
		// querySelector('#id')
		let i = Math.floor(Math.random() * window.generated_divs);
		let element = document.querySelector(`#foo${i}`);
	});

	suite.add("querySelector('.class')", function () {
		// querySelector('.class')
		let i = Math.floor(Math.random() * window.generated_divs);
		let element = document.querySelector(`.foo${i}`);
	});

	suite.add("querySelector('[attr]]')", function () {
		// querySelector('[attr]]')
		let i = Math.floor(Math.random() * window.generated_divs);
		let element = document.querySelector(`[foo${i}]`);
	});

	suite.on("cycle", function (evt) {
		console.log(" - " + evt.target);
	});

	suite.on("complete", function (evt) {
		console.log(new Array(30).join("-"));

		var results = evt.currentTarget.sort(function (a, b) {
			return b.hz - a.hz;
		});

		results.forEach(function (item) {
			console.log((idx + 1) + ". " + item);
		});
	});

	console.log("getElementsByClassName vs getElementById vs querySelector");
	console.log(new Array(30).join("-"));
	suite.run();
});
	<!DOCTYPE html>
	<html>
	<head>
	<meta charset="utf-8"/>
	<title>getElementsByClassName vs getElementById vs querySelector</title>
	<script src="https://cdnjs.cloudflare.com/ajax/libs/benchmark/1.0.0/benchmark.min.js"></script>
	<script src="./suite.js"></script>
	</head>
	<body>
	<h1>Open the console to view the results</h1>
	<h2><code>cmd + alt + j</code> or <code>ctrl + alt + j</code></h2>
	</body>
	</html>
	"use strict";

	(function (factory) {
	if (typeof Benchmark !== "undefined") {
	factory(Benchmark);
	} else {
	factory(require("benchmark"));
	}
	})(function (Benchmark) {
	var suite = new Benchmark.Suite;

	Benchmark.prototype.setup = function () {
	window.generated_divs = 5000;

	let root = document.createElement("div");

	for(let i = 0; i < generated_divs; i++) {
	let el = document.createElement("div");
	el.id = `foo${i}`;
	el.className = `foo${i}`;
	el.setAttribute(`foo${i}`, '');
	root.appendChild(el);
	}

	document.body.appendChild(root);
	};

	Benchmark.prototype.teardown = function () {
	document.body.removeChild(root);
	root = null;
	};

	suite.add("getElementById", function () {
	// getElementById
	let i = Math.floor(Math.random() * window.generated_divs);
	let element = document.getElementById(`foo${i}`);
	});

	suite.add("getElementsByClassName", function () {
	// getElementsByClassName
	let i = Math.floor(Math.random() * window.generated_divs);
	let element = document.getElementsByClassName(`foo${i}`);
	});

	suite.add("querySelector('#id')", function () {
	// querySelector('#id')
	let i = Math.floor(Math.random() * window.generated_divs);
	let element = document.querySelector(`#foo${i}`);
	});

	suite.add("querySelector('.class')", function () {
	// querySelector('.class')
	let i = Math.floor(Math.random() * window.generated_divs);
	let element = document.querySelector(`.foo${i}`);
	});

	suite.add("querySelector('[attr]]')", function () {
	// querySelector('[attr]]')
	let i = Math.floor(Math.random() * window.generated_divs);
	let element = document.querySelector(`[foo${i}]`);
	});

	suite.on("cycle", function (evt) {
	console.log(" - " + evt.target);
	});

	suite.on("complete", function (evt) {
	console.log(new Array(30).join("-"));

	var results = evt.currentTarget.sort(function (a, b) {
	return b.hz - a.hz;
	});

	results.forEach(function (item) {
	console.log((idx + 1) + ". " + item);
	});
	});

	console.log("getElementsByClassName vs getElementById vs querySelector");
	console.log(new Array(30).join("-"));
	suite.run();
	});