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Teacher's comments：
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一、jQuery操作属性
attr() 方法设置或返回被选元素的属性值;
attr（）设置多个属性语法：$('选择器').attr({属性名:值, 属性名:值 ...})
attr必须属性本身自有的属性值
二、jQuery添加元素
元素内部添加
prepend()在被选元素的开头插入内容;
append()在被选元素的结尾插入内容;
元素外部添加
after()在被选元素之后插入内容;
before()在被选元素之前插入内容;
三、jQuery删除元素
remove() 方法删除被选元素及其子元素;
empty() 方法删除被选元素的子元素;
四、案例：评论点赞练习
<!DOCTYPE html>
<html>
<head>
<title>评论功能练习</title>
<meta charset="utf-8">
<link rel="icon" type="image/x-icon" href="static/images/logo.png">
<link rel="stylesheet" type="text/css" href="static/style.css">
<script type="text/javascript" src="static/jquery-3.3.1.min.js"></script>
<script type="text/javascript">
$(function(){
$('.comment').on('keyup',function(){
var len=$(this).val().length;
$(this).parents('.text-box').find('.length').text(140-len);
})
$(document).on('click','.btn',function(){//点击回复按钮
var val=$(this).prev().val()
if(val==''){
alert('对不起，留言不能为空')
}else{
var date=new Date()
var y=date.getFullYear()+'-'+(date.getMonth()+1)+'-'+date.getDate()+' '+date.getHours()+':'+date.getMinutes()+':'+date.getSeconds();
// console.log(y)
var html='<div class="comment-box clearfix" user="self"><img class="myhead" src="static/images/4.jpg" alt=""><div class="comment-content"><p class="comment-text"><span class="user">我:</span>'+val+'你说的都对……</p><p class="comment-time">'+y+'<a href="javascript:;" class="comment-praise" total="1" my="0" style="display: inline-block">1赞</a><a href="javascript:;" class="comment-operate">删除</a></p></div></div>'
//添加评论
$(this).parents('.box').find('.comment-list').append(html)
//清空输入康
$(this).parents('.box').find('.comment').val('')
//初始化输入字数
$(this).parents('.box').find('.length').text('0')
$(this).prev().height(20)
}
})
//动态删除
// $('.comment-operate').on('click',function(){
// if(confirm('确定删除吗？')){
// $(this).parents('.comment-box').remove();
// }
// })
$(document).on('click','.comment-operate',function(){
if(confirm('确定删除么?')){
$(this).parents('.comment-box').remove();
}
})
//给评论框增加高度
$(document).on('click','.comment',function(){
$(this).height(80)
})
//给评论点赞
$(document).on('click','.comment-praise',function(){
var num=parseInt($(this).attr('total'))+1;
$(this).attr('total',num);
$(this).html(num+'赞')
})
//给话题点赞
$(document).on('click','.praise',function(){
$(this).attr('class','praise_2')
})
//删除话题
$(document).on('click','.close',function(){
if(confirm('确定删除么?')){
$(this).parents('.box').remove();
}
})
})
</script>
</head>
<body>
<div id="list">
<div class="box clearfix">
<!-- 删除说说按钮 close-->
<a class="close" href="javascript:;">×</a>
<img class="head" src="static/images/1.png" alt="">
<div class="content">
<div class="main">
<p class="txt">
<span class="user">西门大官人: </span>
~ All the luck is for you. ~
</p>
<img class="pic" src="static/images/img1.jpg" alt="">
</div>
<div class="info clearfix">
<span class="time">02-14 23:01</span>
<!-- 给说说点赞 praise -->
<a class="praise" href="javascript:;">赞</a>
</div>
<div class="praises-total" total="4" style="display: block;">4个人觉得很赞</div>
<!--评论内容-->
<div class="comment-list">
<!-- 每次评论要添加的内容跟标签 -->
<div class="comment-box clearfix" user="self">
<img class="myhead" src="static/images/4.jpg" alt="">
<div class="comment-content">
<p class="comment-text"><span class="user">我:</span>你说的都对……</p>
<p class="comment-time">
2019-01-19 14:36
<a href="javascript:;" class="comment-praise" total="1" my="0" style="display: inline-block">1赞</a>
<a href="javascript:;" class="comment-operate">删除</a>
</p>
</div>
</div>
<!--添加结束-->
</div>
<!--评论内容结束-->
<div class="text-box">
<textarea class="comment" placeholder="评论…"></textarea>
<button class="btn">回 复</button>
<span class="word"><span class="length">0</span>/140</span>
</div>
</div>
</div>
<div class="box clearfix">
<a class="close" href="javascript:;">×</a>
<img class="head" src="static/images/2.jpg" alt=""/>
<div class="content">
<div class="main">
<p class="txt">
<span class="user">欧阳克 : </span>三亚的海滩很漂亮。
</p>
<img class="pic" src="static/images/img5.jpg" alt=""/>
</div>
<div class="info clearfix">
<span class="time">02-14 23:01</span>
<a class="praise" href="javascript:;">赞</a>
</div>
<div class="praises-total" total="0" style="display: none;"></div>
<div class="comment-list">
<div class="comment-box clearfix" user="other">
<img class="myhead" src="static/images/3.png" alt="">
<div class="comment-content">
<p class="comment-text"><span class="user">韦小宝：</span>我也想去三亚。</p>
<p class="comment-time">
2019-01-19 14:36
<a href="javascript:;" class="comment-praise" total="0" my="0">赞</a>
<a href="javascript:;" class="comment-operate">删除</a>
</p>
</div>
</div>
</div>
<div class="text-box">
<textarea class="comment" placeholder="评论…"></textarea>
<button class="btn">回 复</button>
<span class="word"><span class="length">0</span>/140</span>
</div>
</div>
</div>
</div>
</body>
</html>点击 "运行实例" 按钮查看在线实例