使用classList也是理想的

HTML

<div id="box" class="myClass"></div>

JavaScript

const element = document.querySelector("#box");

element.classList.contains("myClass");

这有点过时了，但也许有人会发现我的解决方案很有帮助:

// Fix IE's indexOf Array
if (!Array.prototype.indexOf) {
    Array.prototype.indexOf = function (searchElement) {
        if (this == null) throw new TypeError();
        var t = Object(this);
        var len = t.length >>> 0;
        if (len === 0) return -1;
        var n = 0;
        if (arguments.length > 0) {
            n = Number(arguments[1]);
            if (n != n) n = 0;
            else if (n != 0 && n != Infinity && n != -Infinity) n = (n > 0 || -1) * Math.floor(Math.abs(n));
        }
        if (n >= len) return -1;
        var k = n >= 0 ? n : Math.max(len - Math.abs(n), 0);
        for (; k < len; k++) if (k in t && t[k] === searchElement) return k;
        return -1;
    }
}
// add hasClass support
if (!Element.prototype.hasClass) {
    Element.prototype.hasClass = function (classname) {
        if (this == null) throw new TypeError();
        return this.className.split(' ').indexOf(classname) === -1 ? false : true;
    }
}

Felix's trick of adding spaces to flank the className and the string you're searching for is the right approach to determining whether the elements has the class or not. To have different behaviour according to the class, you may use function references, or functions, within a map: function fn1(element){ /* code for element with class1 */ } function fn2(element){ /* code for element with class2 */ } function fn2(element){ /* code for element with class3 */ } var fns={'class1': fn1, 'class2': fn2, 'class3': fn3}; for(var i in fns) { if(hasClass(test, i)) { fns[i](test); } } for(var i in fns) iterates through the keys within the fns map. Having no break after fnsi allows the code to be executed whenever there is a match - so that if the element has, f.i., class1 and class2, both fn1 and fn2 will be executed. The advantage of this approach is that the code to execute for each class is arbitrary, like the one in the switch statement; in your example all the cases performed a similar operation, but tomorrow you may need to do different things for each. You may simulate the default case by having a status variable telling whether a match was found in the loop or not.

使用classList也是理想的

HTML

<div id="box" class="myClass"></div>

JavaScript

const element = document.querySelector("#box");

element.classList.contains("myClass");

这里有一个小片段，如果你试图检查元素是否包含一个类，而不使用jQuery。

function hasClass(element, className) {
    return element.className && new RegExp("(^|\\s)" + className + "(\\s|$)").test(element.className);
}

这说明元素可能包含多个用空格分隔的类名。

OR

您还可以将此函数分配给元素原型。

Element.prototype.hasClass = function(className) {
    return this.className && new RegExp("(^|\\s)" + className + "(\\s|$)").test(this.className);
};

并像这样触发它(非常类似于jQuery的.hasClass()函数):

document.getElementById('MyDiv').hasClass('active');

简单而有效的解决方法是尝试。包含方法。

test.classList.contains(testClass);