一篇文章告诉你如何用事件委托实现JavaScript留言板功能

用事件委托实现留言板功能。

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }
        body {
            width: 100%;
            height: 100%;
            background: rgb(65, 65, 63);
        }
        .bacground {
            width: 700px;
            height: 100%;
            background: white;
            margin: auto;
            margin-top: 20px;
        }
        .head,
        .pop-head {
            height: 50px;
            font-size: 20px;
            text-align: center;
            line-height: 50px;
        }
        .name {
            width: 640px;
            height: 40px;
            font-size: 20px;
            margin: 10px 28px;
            line-height: 50px;
            border-radius: 8px;
            border: 2px solid rgb(139, 137, 137);
            outline: none;
        }
        .content,
        .pop-reply {
            width: 640px;
            height: 150px;
            font-size: 22px;
            margin: 10px 28px;
            border: 2px solid rgb(139, 137, 137);
            outline: none;
            border-radius: 8px;
            resize: none;
        }
        .btn,
        .pop-btn {
            float: right;
            height: 30px;
            margin-right: 28px;
            border-radius: 6px;
            outline: none;
            font-size: 20px;
            padding: 0 20px;
            background: rgb(169, 238, 255);
        }
        h3 {
            font-size: 20px;
            color: rgb(102, 102, 102);
            background: rgb(205, 221, 248);
            margin-top: 50px;
            line-height: 50px;
            text-indent: 30px;
            font-weight: 545;
        }
        li {
            list-style: none;
            width: 640px;
            font-size: 22px;
            margin: 15px 30px;
        }
        .message-head {
            display: flex;
        }
        .message-head .photo {
            width: 70px;
            height: 70px;
            background: rgb(6, 109, 134);
            display: inline-block;
            border-radius: 50%;
            text-align: center;
            line-height: 70px;
            overflow: hidden;
        }
        .message-head .time {
            margin-left: 12px;
        }
        .liuyan,
        .reply p {
            width: 560px;
            /* height: 76px; */
            line-height: 50px;
            display: block;
            background: rgb(205, 221, 248);
            font-size: 20px;
            margin-left: 80px;
            border-radius: 8px;
            text-indent: 15px;
        }
        .delete {
            width: 60px;
            height: 30px;
            display: block;
            line-height: 30px;
            margin-left: 580px;
            /* margin-bottom: 0px; */
            border-radius: 6px;
            outline: none;
            font-size: 15px;
            background: rgb(169, 238, 255);
        }
        .answer {
            width: 60px;
            height: 30px;
            display: block;
            line-height: 30px;
            margin-top: -29px;
            margin-left: 515px;
            border-radius: 6px;
            outline: none;
            font-size: 15px;
            background: rgb(169, 238, 255);
        }
        .popup {
            width: 100vw;
            height: 100vh;
            position: fixed;
            background: rgba(0, 0, 0, .3);
            left: 0;
            top: 0;
            z-index: 10;
            display: flex;
            align-items: center;
            justify-content: center;
            display: none;
        }
        .pop-content {
            width: 700px;
            background: #fff;
            border-radius: 10px;
            overflow: hidden;
            padding-bottom: 20px;
        }
        .reply p {
            margin-top: 10px;
            background: rgba(100, 100, 100, .1);
        }
    </style>
</head>
<body>
    <div class="bacground">
        <div class="head">留言板</div>
        <input class="name" type="text" placeholder="请输入您的昵称">
        <textarea class="content" placeholder="请保持言论文明......"></textarea>
        <button class="btn">留言</button>
        <h3>大家在说</h3>
        <ul class="text">
            <!-- <li>
			<div class="message-head">
			<span class="photo">系统</span>
			<p class="time">2019-9-27 0:47:38</p>
			</div>
			<p class="liuyan">测试留言</p>
			<div class="reply">
			<p>测试回复</p>
			</div>
			<button class="delete">Delete</button>
			<button class="answer">Answer</button>
		</li> -->
        </ul>
    </div>
    <div class="popup">
        <div class="pop-content">
            <div class="pop-head">回复板</div>
            <textarea class="pop-reply" placeholder="请保持言论文明......"></textarea>
            <button class="pop-btn huiFu">回复</button>
            <button class="pop-btn quXiao">取消</button>
        </div>
    </div>
    <script>
        //在事件委托中,每一个if都相当于一个独立的函数,因为每一次点击都会重新触发事件处理函数
        var oAns ;
        //分析:事件委托给谁? --- 共同的父元素
        document.onclick = function (e) {
            //事件处理对象,兼容IE8及以下版本的浏览器
            e = e || event ;
            // target目标  --- 具体是由哪个标签触发的
            var target = e.target ;

            //留言
            if(target.className === "btn"){
                //获取对象
                var nickname = $(".name").value ;
                var content = $(".content").value ;
                //判断输入是否为空
                if(nickname && content){
                    //创建一个标签
                    var oLi = document.createElement("li") ;
                    //插入新内容
                    oLi.innerHTML = `
                    <div class="message-head">
                        <span class="photo">${nickname}</span>
                        <p class="time">2019-9-27 0:47:38</p>
                    </div>
                    <p class="liuyan">${content}</p>
                    <div class="reply">
                    </div>
                    <button class="delete">Delete</button>
                    <button class="answer">Answer</button>
                    `  
                    //将最新的留言插入到最上面
                    $(".text").insertBefore(oLi , $(".text").firstChild) ;
                    //倒计时
                    clock(target , 3) ;
                    //留言完后清空留言板内容
                    $(".content").value = "" ;
                }else{
                    alert("输入不能为空!")
                }
                return
            }
            //删除
            if(target.className === "delete"){
                //删除留言
                target.parentNode.remove() ;
                return
            }
            //回复
            if(target.className === "answer"){
                //显示弹窗
                $(".popup").style.display = "flex" ;
                //找到回复留言的地方
                oAns = target.previousElementSibling.previousElementSibling ;
                return 
            }
            //确认回复
            if(target.className === "pop-btn huiFu"){
                //拿到回复的内容
                var huiFuContent = $(".pop-reply").value ;
                if(huiFuContent){
                    //创建一个标签
                    var oP = document.createElement("p") ;
                    //将内容插入标签中
                    oP.innerHTML = huiFuContent ;
                    //将回复插入到留言的地方
                    oAns.appendChild(oP) ;
                }
                //关闭弹窗
                $(".popup").style.display = "none" ;
                return
            }
            //取消回复
            if(target.className === "pop-btn quXiao"){
                $(".popup").style.display = "none" ;
                return
            }
        }
        //倒计时
        function clock(ele , time){
            if(!ele.disabled){
                ele.disabled = true ;
                ele.innerHTML = time + "s后可再次留言" ;
                var t = setInterval(function () {
                    time-- ;
                    ele.innerHTML = time + "s后可再次留言" ;
                    if(time <= 0){
                        clearInterval(t) ;
                        ele.disabled = false ;
                        ele.innerHTML = "留言" ;
                    }
                },1000)
            }
        }
        //获取对象
        function $(selector){
            return document.querySelector(selector) ;
        }
    </script>
</body>
</html>

总结

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