使用jQuery可以给元素很方便的添加class和删除class等操作，现在原生的JavaScript也可以实现这个方法了。使用classList可以方便的添加class、删除class、查询class等。
语法：
let elementClass = element.classList;
elementClasses 是一个 DOMTokenList 表示 element 的类属性 。如果类属性未设置或为空，那么 elementClasses.length 返回 0。element.classList 本身是只读的，虽然你可以使用 add() 和 remove() 方法修改它。
方法：
add( String [, String] )
添加指定的类值。如果这些类已经存在于元素的属性中，那么它们将被忽略。
remove( String [,String] )
删除指定的类值。
item ( Number )
按集合中的索引返回类值。
toggle ( String [, force] )
当只有一个参数时：切换 class value; 即如果类存在，则删除它并返回false，如果不存在，则添加它并返回true。
当存在第二个参数时：如果第二个参数的计算结果为true，则添加指定的类值，如果计算结果为false，则删除它
contains( String )
检查元素的类属性中是否存在指定的类值。
示例：
// div是具有class =“foo bar”的<div>元素的对象引用
div.classList.remove("foo");
div.classList.add("anotherclass");
// 如果visible被设置则删除它，否则添加它
div.classList.toggle("visible");
// 添加/删除 visible，取决于测试条件，i小于10
div.classList.toggle("visible", i < 10);
alert(div.classList.contains("foo"));
//添加或删除多个类
div.classList.add("foo","bar");
div.classList.remove("foo", "bar");
兼容性
不兼容Android2.3和iOS4.2的，在移动端上想使用也是有点头疼啊。IE系列的更别说IE9和IE8了。所以目前来看，还是无法在实际中放心的使用，只能用于某些特定的项目等。不过我们可以通过一些shim来实现，或者最下方给出的原生javascript实现。
跨浏览器javascript shim
https://github.com/eligrey/classList.js/blob/master/classList.js
if ("document" in self) {
// Full polyfill for browsers with no classList support
if (!("classList" in document.createElement("_"))) {
(function (view) {
"use strict";
if (!('Element' in view)) return;
var
classListProp = "classList"
, protoProp = "prototype"
, elemCtrProto = 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.getAttribute("class") || "")
, classes = trimmedClasses ? trimmedClasses.split(/\s+/) : []
, i = 0
, len = classes.length
;
for (; i < len; i++) {
this.push(classes[i]);
}
this._updateClassName = function () {
elem.setAttribute("class", 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 () {
var
tokens = arguments
, i = 0
, l = tokens.length
, token
, updated = false
;
do {
token = tokens[i] + "";
if (checkTokenAndGetIndex(this, token) === -1) {
this.push(token);
updated = true;
}
}
while (++i < l);
if (updated) {
this._updateClassName();
}
};
classListProto.remove = function () {
var
tokens = arguments
, i = 0
, l = tokens.length
, token
, updated = false
, index
;
do {
token = tokens[i] + "";
index = checkTokenAndGetIndex(this, token);
while (index !== -1) {
this.splice(index, 1);
updated = true;
index = checkTokenAndGetIndex(this, token);
}
}
while (++i < l);
if (updated) {
this._updateClassName();
}
};
classListProto.toggle = function (token, force) {
token += "";
var
result = this.contains(token)
, method = result ?
force !== true && "remove"
:
force !== false && "add"
;
if (method) {
this[method](token);
}
if (force === true || force === false) {
return force;
} else {
return !result;
}
};
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));
} else {
// There is full or partial native classList support, so just check if we need
// to normalize the add/remove and toggle APIs.
(function () {
"use strict";
var testElement = document.createElement("_");
testElement.classList.add("c1", "c2");
// Polyfill for IE 10/11 and Firefox <26, where classList.add and
// classList.remove exist but support only one argument at a time.
if (!testElement.classList.contains("c2")) {
var createMethod = function(method) {
var original = DOMTokenList.prototype[method];
DOMTokenList.prototype[method] = function(token) {
var i, len = arguments.length;
for (i = 0; i < len; i++) {
token = arguments[i];
original.call(this, token);
}
};
};
createMethod('add');
createMethod('remove');
}
testElement.classList.toggle("c3", false);
// Polyfill for IE 10 and Firefox <24, where classList.toggle does not
// support the second argument.
if (testElement.classList.contains("c3")) {
var _toggle = DOMTokenList.prototype.toggle;
DOMTokenList.prototype.toggle = function(token, force) {
if (1 in arguments && !this.contains(token) === !force) {
return force;
} else {
return _toggle.call(this, token);
}
};
}
testElement = null;
}());
}
}
原生JavaScript
类似于jQuery库的使用方式，使用className通过正则来添加或者删除class。
addClass、removeClass、toggleClass、hasClass
function hasClass(obj, cls) {
return obj.className.match(new RegExp('(\\s|^)' + cls + '(\\s|$)'));
}
function addClass(obj, cls) {
if (!this.hasClass(obj, cls)) obj.className += " " + cls;
}
function removeClass(obj, cls) {
if (hasClass(obj, cls)) {
var reg = new RegExp('(\\s|^)' + cls + '(\\s|$)');
obj.className = obj.className.replace(reg, ' ');
}
}
function toggleClass(obj,cls){
if(hasClass(obj,cls)){
removeClass(obj, cls);
}else{
addClass(obj, cls);
}
}
