闭包存循环的索引值

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>闭包存循环的索引值</title>
    <style type="text/css">
        li{
            height: 30px;
            background-color: gold;
            margin-bottom: 10px;
        }
    </style>
    <script type="text/javascript">
        //闭包的用途：存循环的索引值
        window.onload = function(){
            var aLi = document.getElementsByTagName('li');
            // alert(aLi.length);//8
            for(var i=0; i<aLi.length; i++){
                /*
                aLi[i].onclick = function(){
                    alert(i);//每个li都弹出8，因为点击时循环已完毕，i最后为8
                }
                */
                (function(k){//这里的k是形参
                    aLi[k].onclick = function(){
                        alert(k);//弹出每个li的索引值
                    }
                })(i);//这里的i是实参
            }
        }
    </script>
</head>
<body>
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
        <li>6</li>
        <li>7</li>
        <li>8</li>
    </ul>
</body>
</html>

闭包做私有变量计数器

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>闭包做私有变量计数器</title>
    <script type="text/javascript">
        //闭包的用途：私有变量计数器
        var count = (function(){
            var a = 0;
            function bb(){
                a++;
                return a;
            }
            return bb;
        })();

        //每调用一次count，a就自增一次
        alert(count());//1
        alert(count());//2
        var c = count();
        alert(c);//3
    </script>
</head>
<body>
    
</body>
</html>

闭包做选项卡



<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>闭包做选项卡</title>
    <style type="text/css">
        .btns{
            width: 500px;
            height: 50px;
        }
        /*选项卡的样式*/
        .btns input{
            width: 100px;
            height: 50px;
            background-color: #ddd;/*默认灰色*/
            color: #666;
            border: 0px;
        }
        /*被选中的选项卡的样式*/
        .btns input.cur{
            background-color: gold;
        }
        /*内容区的样式*/
        .contents div{
            width: 500px;
            height: 300px;
            background-color: gold;
            display: none;/*默认隐藏*/
            line-height: 300px;
            text-align: center;
        }
        /*被选中的内容区的样式*/
        .contents div.active{
            display: block;
        }
    </style>
    <script type="text/javascript">
        //闭包做选项卡
        window.onload = function(){
            var aBtn = document.getElementById('btns').getElementsByTagName('input');
            var aCon = document.getElementById('contents').getElementsByTagName('div');
            // alert(aCon.length);
            //循环所有的选项卡按钮
            for(var i=0; i<aBtn.length; i++){
                (function(i){
                    //给每个选项卡按钮添加点击事件
                    aBtn[i].onclick = function(){
                        //遍历所有选项卡按钮
                        for(var j=0; j<aBtn.length; j++){
                            //将每个选项卡按钮都设为灰色
                            aBtn[j].className = '';
                            //将每个内容区都隐藏
                            aCon[j].className = '';
                        }
                        //this代表当前点击的Button对象
                        this.className = 'cur';//当前点击的按钮为金色
                        // alert(i);//不加闭包时，不管点哪个按钮，i都等于3
                        //加闭包保存了索引值才有效
                        aCon[i].className = 'active';//当前点击的按钮对应的内容显示
                    }
                })(i);
            }
        }
    </script>
</head>
<body>
    <div class="btns" id="btns">
        <input type="button" value="tab01" class="cur">
        <input type="button" value="tab02">
        <input type="button" value="tab03">
    </div>
    <div class="contents" id="contents">
        <div class="active">tab文字内容一</div>
        <div>tab文字内容二</div>
        <div>tab文字内容三</div>
    </div>
</body>
</html>