闭包跟作用域相关的，ECMAScript 允许使用内部函数，即函数定义和函数表达式位于另一个函数的函数体内。内部函数可以访问它们所在的外部函数中声明的所有局部变量、参数和声明的其他内部函数。当其中一个这样的内部函数在包含它们的外部函数之外被调用时，就会形成闭包。
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<style>
li{
height:30px;
background: red;
margin:10px;
}
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<body>
<ul>
<li>1</li>
<li>2</li>
<li>3</li>
</ul>
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*{
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ul{
margin:0;
list-style: none;
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#tit li{
float:left;
width:90px;
height:40px;
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.tit{
background: red;
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width:270px;
line-height:300px;
border:1px solid red;
font-size:50px;
color:red;
text-align:center;
}
.con{
display:none;
}
.show{
display:block;
}
</style>
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<ul id="tit">
<li class="tit select">1</li>
<li class="tit">2</li>
<li class="tit">3</li>
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<div id="con">
<div class="con show">1</div>
<div class="con">2</div>
<div class="con">3</div>
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<script>
var tits = document.getElementById('tit').getElementsByTagName('li'),
cons = document.getElementById('con').getElementsByTagName('div');
for (