Question

当包含触发器类的div标签发生更改时，我希望我的活动触发。

我不知道如何让它听取课程'添加事件。

<div id="test">test</div>

<script type="text/javascript">
    document.getElementById.setAttribute("class", "trigger");

    function workOnClassAdd() {
       alert("I'm triggered");
    }
</script>

Answer 1

那么有mutation events，但它们已被弃用，未来会有Mutation Observers，但很长一段时间它们都不会得到完全支持。那么你能在同一时间做什么呢？

您可以使用计时器检查元素。

function addClassNameListener(elemId, callback) {
    var elem = document.getElementById(elemId);
    var lastClassName = elem.className;
    window.setInterval( function() {   
       var className = elem.className;
        if (className !== lastClassName) {
            callback();   
            lastClassName = className;
        }
    },10);
}

正在运行示例：jsFiddle

Answer 2

未来就在这里，您可以使用MutationObserver界面监视特定类别的更改。

let targetNode = document.getElementById('test')

function workOnClassAdd() {
    alert("I'm triggered when the class is added")
}

function workOnClassRemoval() {
    alert("I'm triggered when the class is removed")
}

// watch for a specific class change
let classWatcher = new ClassWatcher(targetNode, 'trigger', workOnClassAdd, workOnClassRemoval)

// tests:
targetNode.classList.add('trigger') // triggers workOnClassAdd callback
targetNode.classList.add('trigger') // won't trigger (class is already exist)
targetNode.classList.add('another-class') // won't trigger (class is not watched)
targetNode.classList.remove('trigger') // triggers workOnClassRemoval callback
targetNode.classList.remove('trigger') // won't trigger (class was already removed)
targetNode.setAttribute('disabled', true) // won't trigger (the class is unchanged)

我用一个简单的类包装了 MutationObserver ：

class ClassWatcher {

    constructor(targetNode, classToWatch, classAddedCallback, classRemovedCallback) {
        this.targetNode = targetNode
        this.classToWatch = classToWatch
        this.classAddedCallback = classAddedCallback
        this.classRemovedCallback = classRemovedCallback
        this.observer = null
        this.lastClassState = targetNode.classList.contains(this.classToWatch)

        this.init()
    }

    init() {
        this.observer = new MutationObserver(this.mutationCallback)
        this.observe()
    }

    observe() {
        this.observer.observe(this.targetNode, { attributes: true })
    }

    disconnect() {
        this.observer.disconnect()
    }

    mutationCallback = mutationsList => {
        for(let mutation of mutationsList) {
            if (mutation.type === 'attributes' && mutation.attributeName === 'class') {
                let currentClassState = mutation.target.classList.contains(this.classToWatch)
                if(this.lastClassState !== currentClassState) {
                    this.lastClassState = currentClassState
                    if(currentClassState) {
                        this.classAddedCallback()
                    }
                    else {
                        this.classRemovedCallback()
                    }
                }
            }
        }
    }
}

Answer 3

这是一个简单的基本示例，说明如何在Class属性更改时触发回调
MutationObserver API

const attrObserver = new MutationObserver((mutations) => {
  mutations.forEach(mu => {
    if (mu.type !== "attributes" && mu.attributeName !== "class") return;
    console.log("class was modified!");
  });
});

const ELS_test = document.querySelectorAll(".test");
ELS_test.forEach(el => attrObserver.observe(el, {attributes: true}));


// Example of Buttons toggling several .test classNames
document.querySelectorAll(".btn").forEach(btn => {
  btn.addEventListener("click", () => ELS_test.forEach(el => el.classList.toggle(btn.dataset.class)));
});

.blue {background: blue;}
.gold {color: gold;}

<div class="test">TEST DIV</div>
<button class="btn" data-class="blue">BACKGROUND</button>
<button class="btn" data-class="gold">COLOR</button>

类更改的事件触发器

3 个答案: