Element.classList

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范例
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Element.classList is a read-only property that returns a live DOMTokenList collection of the class attributes of the element. This can then be used to manipulate the class list.

使用 classList is a convenient alternative to accessing an element's list of classes as a space-delimited string via element.className .

句法

const elementClasses = elementNodeReference.classList;

A DOMTokenList representing the contents of the element's class attribute. If the class attribute is not set or empty, it returns an empty DOMTokenList , i.e. a DOMTokenList 采用 length property equal to 0 .

DOMTokenList itself is read-only, although you can modify it using the add() and remove() 方法。

范例

const div = document.createElement('div');
div.className = 'foo';
// our starting state: <div class="foo"></div>
console.log(div.outerHTML);
// use the classList API to remove and add classes
div.classList.remove("foo");
div.classList.add("anotherclass");
// <div class="anotherclass"></div>
console.log(div.outerHTML);
// if visible is set remove it, otherwise add it
div.classList.toggle("visible");
// add/remove visible, depending on test conditional, i less than 10
div.classList.toggle("visible", i < 10 );
console.log(div.classList.contains("foo"));
// add or remove multiple classes
div.classList.add("foo", "bar", "baz");
div.classList.remove("foo", "bar", "baz");
// add or remove multiple classes using spread syntax
const cls = ["foo", "bar"];
div.classList.add(...cls);
div.classList.remove(...cls);
// replace class "foo" with class "bar"
div.classList.replace("foo", "bar");

Versions of Firefox before 26 do not implement the use of several arguments in the add/remove/toggle methods. See https://bugzilla.mozilla.org/show_bug.cgi?id=814014

Polyfill

传统 onpropertychange event can be used to create a living classList mockup thanks to a Element.prototype.className property that fires the specified event once it is changed.

The following polyfill for both classList and DOMTokenList ensures full compliance (coverage) for all standard methods and properties of Element.prototype.classList for IE10 - IE11 browsers plus nearly compliant behavior for IE 6-9 . Check it out:

// 1. String.prototype.trim polyfill
if (!"".trim) String.prototype.trim = function(){ return this.replace(/^[\s]+|[\s]+$/g, ''); };
(function(window){"use strict"; // prevent global namespace pollution
if(!window.DOMException) (DOMException = function(reason){this.message = reason}).prototype = new Error;
var wsRE = /[\11\12\14\15\40]/, wsIndex = 0, checkIfValidClassListEntry = function(O, V) {
  if (V === "") throw new DOMException(
    "Failed to execute '" + O + "' on 'DOMTokenList': The token provided must not be empty." );
  if((wsIndex=V.search(wsRE))!==-1) throw new DOMException("Failed to execute '"+O+"' on 'DOMTokenList': " +
    "The token provided ('"+V[wsIndex]+"') contains HTML space characters, which are not valid in tokens.");
}
// 2. Implement the barebones DOMTokenList livelyness polyfill
if (typeof DOMTokenList !== "function") (function(window){
    var document = window.document, Object = window.Object, hasOwnProp = Object.prototype.hasOwnProperty;
    var defineProperty = Object.defineProperty, allowTokenListConstruction = 0, skipPropChange = 0;
    function DOMTokenList(){
        if (!allowTokenListConstruction) throw TypeError("Illegal constructor"); // internally let it through
    }
    DOMTokenList.prototype.toString = DOMTokenList.prototype.toLocaleString = function(){return this.value};
    DOMTokenList.prototype.add = function(){
        a: for(var v=0, argLen=arguments.length,val="",ele=this[" uCL"],proto=ele[" uCLp"]; v!==argLen; ++v) {
            val = arguments[v] + "", checkIfValidClassListEntry("add", val);
            for (var i=0, Len=proto.length, resStr=val; i !== Len; ++i)
                if (this[i] === val) continue a; else resStr += " " + this[i];
            this[Len] = val, proto.length += 1, proto.value = resStr;
        }
        skipPropChange = 1, ele.className = proto.value, skipPropChange = 0;
    };
    DOMTokenList.prototype.remove = function(){
        for (var v=0, argLen=arguments.length,val="",ele=this[" uCL"],proto=ele[" uCLp"]; v !== argLen; ++v) {
            val = arguments[v] + "", checkIfValidClassListEntry("remove", val);
            for (var i=0, Len=proto.length, resStr="", is=0; i !== Len; ++i)
                if(is){ this[i-1]=this[i] }else{ if(this[i] !== val){ resStr+=this[i]+" "; }else{ is=1; } }
            if (!is) continue;
            delete this[Len], proto.length -= 1, proto.value = resStr;
        }
        skipPropChange = 1, ele.className = proto.value, skipPropChange = 0;
    };
    window.DOMTokenList = DOMTokenList;
    function whenPropChanges(){
        var evt = window.event, prop = evt.propertyName;
        if ( !skipPropChange && (prop==="className" || (prop==="classList" && !defineProperty)) ) {
            var target = evt.srcElement, protoObjProto = target[" uCLp"], strval = "" + target[prop];
            var tokens=strval.trim().split(wsRE), resTokenList=target[prop==="classList"?" uCL":"classList"];
            var oldLen = protoObjProto.length;
            a: for(var cI = 0, cLen = protoObjProto.length = tokens.length, sub = 0; cI !== cLen; ++cI){
                for(var innerI=0; innerI!==cI; ++innerI) if(tokens[innerI]===tokens[cI]) {sub++; continue a;}
                resTokenList[cI-sub] = tokens[cI];
            }
            for (var i=cLen-sub; i < oldLen; ++i) delete resTokenList[i]; //remove trailing indexs
            if(prop !== "classList") return;
            skipPropChange = 1, target.classList = resTokenList, target.className = strval;
            skipPropChange = 0, resTokenList.length = tokens.length - sub;
        }
    }
    function polyfillClassList(ele){
        if (!ele || !("innerHTML" in ele)) throw TypeError("Illegal invocation");
        ele.detachEvent( "onpropertychange", whenPropChanges ); // prevent duplicate handler infinite loop
        allowTokenListConstruction = 1;
        try{ function protoObj(){} protoObj.prototype = new DOMTokenList(); }
        finally { allowTokenListConstruction = 0 }
        var protoObjProto = protoObj.prototype, resTokenList = new protoObj();
        a: for(var toks=ele.className.trim().split(wsRE), cI=0, cLen=toks.length, sub=0; cI !== cLen; ++cI){
            for (var innerI=0; innerI !== cI; ++innerI) if (toks[innerI] === toks[cI]) { sub++; continue a; }
            this[cI-sub] = toks[cI];
        }
        protoObjProto.length = cLen-sub, protoObjProto.value = ele.className, protoObjProto[" uCL"] = ele;
        if (defineProperty) { defineProperty(ele, "classList", { // IE8 & IE9 allow defineProperty on the DOM
            enumerable:   1, get: function(){return resTokenList},
            configurable: 0, set: function(newVal){
                skipPropChange = 1, ele.className = protoObjProto.value = (newVal += ""), skipPropChange = 0;
                var toks = newVal.trim().split(wsRE), oldLen = protoObjProto.length;
                a: for(var cI = 0, cLen = protoObjProto.length = toks.length, sub = 0; cI !== cLen; ++cI){
                    for(var innerI=0; innerI!==cI; ++innerI) if(toks[innerI]===toks[cI]) {sub++; continue a;}
                    resTokenList[cI-sub] = toks[cI];
                }
                for (var i=cLen-sub; i < oldLen; ++i) delete resTokenList[i]; //remove trailing indexs
            }
        }); defineProperty(ele, " uCLp", { // for accessing the hidden prototype
            enumerable: 0, configurable: 0, writeable: 0, value: protoObj.prototype
        }); defineProperty(protoObjProto, " uCL", {
            enumerable: 0, configurable: 0, writeable: 0, value: ele
        }); } else { ele.classList=resTokenList, ele[" uCL"]=resTokenList, ele[" uCLp"]=protoObj.prototype; }
        ele.attachEvent( "onpropertychange", whenPropChanges );
    }
    try { // Much faster & cleaner version for IE8 & IE9:
        // Should work in IE8 because Element.prototype instanceof Node is true according to the specs
        window.Object.defineProperty(window.Element.prototype, "classList", {
            enumerable: 1,   get: function(val){
                                 if (!hasOwnProp.call(this, "classList")) polyfillClassList(this);
                                 return this.classList;
                             },
            configurable: 0, set: function(val){this.className = val}
        });
    } catch(e) { // Less performant fallback for older browsers (IE 6-8):
        window[" uCL"] = polyfillClassList;
        // the below code ensures polyfillClassList is applied to all current and future elements in the doc.
        document.documentElement.firstChild.appendChild(document.createElement('style')).styleSheet.cssText=(
            '_*{x-uCLp:expression(!this.hasOwnProperty("classList")&&window[" uCL"](this))}' + //  IE6
            '[class]{x-uCLp/**/:expression(!this.hasOwnProperty("classList")&&window[" uCL"](this))}' //IE7-8
        );
    }
})(window);
// 3. Patch in unsupported methods in DOMTokenList
(function(DOMTokenListProto, testClass){
    if (!DOMTokenListProto.item) DOMTokenListProto.item = function(i){
        function NullCheck(n) {return n===void 0 ? null : n} return NullCheck(this[i]);
    };
    if (!DOMTokenListProto.toggle || testClass.toggle("a",0)!==false) DOMTokenListProto.toggle=function(val){
        if (arguments.length > 1) return (this[arguments[1] ? "add" : "remove"](val), !!arguments[1]);
        var oldValue = this.value;
        return (this.remove(oldValue), oldValue === this.value && (this.add(val), true) /*|| false*/);
    };
    if (!DOMTokenListProto.replace || typeof testClass.replace("a", "b") !== "boolean")
        DOMTokenListProto.replace = function(oldToken, newToken){
            checkIfValidClassListEntry("replace", oldToken), checkIfValidClassListEntry("replace", newToken);
            var oldValue = this.value;
            return (this.remove(oldToken), this.value !== oldValue && (this.add(newToken), true));
        };
    if (!DOMTokenListProto.contains) DOMTokenListProto.contains = function(value){
        for (var i=0,Len=this.length; i !== Len; ++i) if (this[i] === value) return true;
        return false;
    };
    if (!DOMTokenListProto.forEach) DOMTokenListProto.forEach = function(f){
        if (arguments.length === 1) for (var i = 0, Len = this.length; i !== Len; ++i) f( this[i], i, this);
        else for (var i=0,Len=this.length,tArg=arguments[1]; i !== Len; ++i) f.call(tArg, this[i], i, this);
    };
    if (!DOMTokenListProto.entries) DOMTokenListProto.entries = function(){
        var nextIndex = 0, that = this;
        return {next: function() {
            return nextIndex<that.length ? {value: [nextIndex, that[nextIndex++]], done: false} : {done: true};
        }};
    };
    if (!DOMTokenListProto.values) DOMTokenListProto.values = function(){
        var nextIndex = 0, that = this;
        return {next: function() {
            return nextIndex<that.length ? {value: that[nextIndex++], done: false} : {done: true};
        }};
    };
    if (!DOMTokenListProto.keys) DOMTokenListProto.keys = function(){
        var nextIndex = 0, that = this;
        return {next: function() {
            return nextIndex<that.length ? {value: nextIndex++, done: false} : {done: true};
        }};
    };
})(window.DOMTokenList.prototype, window.document.createElement("div").classList);
})(window);

告诫

The polyfill is limited in functionality. It's currently unable to polyfill out-of-document-elements (e.g. elements created by document.createElement before they are appended to a parent node) in IE6-7.

However, it should work just fine in IE9. A major discrepancy between the polyfilled version of classList and the W3 specs is that for IE6-8, there is no way to create an immutable object (an object whose properties cannot be directly modified). In IE9, however, it is possible through extending the prototype, freezing the visible object, and overwritting native property methods. However, such actions would not work in IE6-IE8 and, in IE9, slow the performance of the entire webpage to a snail's crawl, making these modifications completely impractical for this polyfill.

A minor note is that in IE6-7, this polyfill uses the window[" uCL"] property on the window object for communicating with the CSS expressions, the x-uCLp css property on all elements, and the element[" uCL"] property on all elements to allow garbage collection and boost performance. In all polyfilled browsers (IE6-9), an additional element[" uCLp"] property is added to element to ensure standards compliant prototyping, and a DOMTokenList[" uCL"] property is added to each element["classList"] object to ensure that the DOMTokenList is bounded to its own element.

规范

规范	状态	注释
DOM The definition of 'Element.classList' in that specification.	实时标准	初始定义
DOM4 The definition of 'Element.classList' in that specification.	过时

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`classList`	Chrome 8	Edge 16 16 不支持 12 — 16 Not supported for SVG elements.	Firefox 3.6	IE 部分支持 10 部分支持 10 Not supported for SVG elements.	Opera 11.5	Safari 6	WebView Android ≤37	Chrome Android 18	Firefox Android 4	Opera Android 11.5	Safari iOS 5	Samsung Internet Android 1.0
Multiple arguments for `add()` & `remove()`	Chrome 24	Edge 12	Firefox 26	IE No	Opera 15	Safari 7	WebView Android ≤37	Chrome Android 25	Firefox Android 26	Opera Android 14	Safari iOS 7	Samsung Internet Android 1.5
`replace()`	Chrome 61	Edge 17	Firefox 49	IE No	Opera ?	Safari No	WebView Android 61	Chrome Android 61	Firefox Android 49	Opera Android ?	Safari iOS No	Samsung Internet Android 8.0
`toggle()` method's second argument	Chrome 24	Edge 12	Firefox 24	IE No	Opera 15	Safari 7	WebView Android Yes	Chrome Android Yes	Firefox Android 24	Opera Android ?	Safari iOS 7	Samsung Internet Android Yes

图例

完整支持
部分支持
不支持
兼容性未知 ?

另请参阅

元数据

最后修改： Apr 6, 2020

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句法

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范例

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告诫

规范

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图例

另请参阅

相关话题