Old JS vs Modern JS vs jQuery to add a class

JavaScript performance comparison

Revision 3 of this test case created by

Preparation code

<body>
<h1>Just a simple test</h1>
</body>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
    

Preparation code output

<body> <h1>Just a simple test</h1> </body>

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Testing in CCBot 2.0.0 / Other 0.0.0
Test Ops/sec
jQuery
$('html').addClass('js');
pending…
modern JS
/*
 * classList.js: Cross-browser full element.classList implementation.
 * 2011-06-15
 *
 * By Eli Grey, http://eligrey.com
 * Public Domain.
 * NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
 */

/*global self, document, DOMException */

/*! @source http://purl.eligrey.com/github/classList.js/blob/master/classList.js*/

if (typeof document !== "undefined" && !("classList" in document.createElement("a"))) {

(function (view) {


"use strict";

var
	  classListProp = "classList"
	, protoProp = "prototype"
	, elemCtrProto = (view.HTMLElement || view.Element)[protoProp]
	, objCtr = Object
	, strTrim = String[protoProp].trim || function () {
		return this.replace(/^\s+|\s+$/g, "");
	}
	, arrIndexOf = Array[protoProp].indexOf || function (item) {
		var
			  i = 0
			, len = this.length
		;
		for (; i < len; i++) {
			if (i in this && this[i] === item) {
				return i;
			}
		}
		return -1;
	}
	// Vendors: please allow content code to instantiate DOMExceptions
	, DOMEx = function (type, message) {
		this.name = type;
		this.code = DOMException[type];
		this.message = message;
	}
	, checkTokenAndGetIndex = function (classList, token) {
		if (token === "") {
			throw new DOMEx(
				  "SYNTAX_ERR"
				, "An invalid or illegal string was specified"
			);
		}
		if (/\s/.test(token)) {
			throw new DOMEx(
				  "INVALID_CHARACTER_ERR"
				, "String contains an invalid character"
			);
		}
		return arrIndexOf.call(classList, token);
	}
	, ClassList = function (elem) {
		var
			  trimmedClasses = strTrim.call(elem.className)
			, classes = trimmedClasses ? trimmedClasses.split(/\s+/) : []
			, i = 0
			, len = classes.length
		;
		for (; i < len; i++) {
			this.push(classes[i]);
		}
		this._updateClassName = function () {
			elem.className = this.toString();
		};
	}
	, classListProto = ClassList[protoProp] = []
	, classListGetter = function () {
		return new ClassList(this);
	}
;
// Most DOMException implementations don't allow calling DOMException's toString()
// on non-DOMExceptions. Error's toString() is sufficient here.
DOMEx[protoProp] = Error[protoProp];
classListProto.item = function (i) {
	return this[i] || null;
};
classListProto.contains = function (token) {
	token += "";
	return checkTokenAndGetIndex(this, token) !== -1;
};
classListProto.add = function (token) {
	token += "";
	if (checkTokenAndGetIndex(this, token) === -1) {
		this.push(token);
		this._updateClassName();
	}
};
classListProto.remove = function (token) {
	token += "";
	var index = checkTokenAndGetIndex(this, token);
	if (index !== -1) {
		this.splice(index, 1);
		this._updateClassName();
	}
};
classListProto.toggle = function (token) {
	token += "";
	if (checkTokenAndGetIndex(this, token) === -1) {
		this.add(token);
	} else {
		this.remove(token);
	}
};
classListProto.toString = function () {
	return this.join(" ");
};

if (objCtr.defineProperty) {
	var classListPropDesc = {
		  get: classListGetter
		, enumerable: true
		, configurable: true
	};
	try {
		objCtr.defineProperty(elemCtrProto, classListProp, classListPropDesc);
	} catch (ex) { // IE 8 doesn't support enumerable:true
		if (ex.number === -0x7FF5EC54) {
			classListPropDesc.enumerable = false;
			objCtr.defineProperty(elemCtrProto, classListProp, classListPropDesc);
		}
	}
} else if (objCtr[protoProp].__defineGetter__) {
	elemCtrProto.__defineGetter__(classListProp, classListGetter);
}

}(self));

}

document.querySelector('html').classList.add('js');
pending…
old style js
document.getElementsByTagName('html')[0].className += ' hasJS';
pending…

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Just a simple test