如何实现复选框的全选和反选？1.实现全选和全不选用全选复选框的状态，赋值给下面的所有复选框 2. 实现复选框全部选中，

<style>
        * {
            margin: 0;
            padding: 0;
        }

        table {
            border-collapse: collapse;
            border-spacing: 0;
            border: 1px solid #c0c0c0;
            width: 500px;
            margin: 100px auto;
            text-align: center;
        }

        th {
            background-color: #09c;
            font: bold 16px '微软雅黑';
            color: #fff;
            height: 24px;
        }

        td {
            border: 1px solid #d0d0d0;
            color: #404060;
            padding: 10px;
        }

        .allCheck {
            width: 80px;
        }
    </style>
</head>

<body>

    <table>
        <tr>
            <th class="allCheck">
                <input type="checkbox" name="" id="checkAll" />
                <span class="all">全选</span>
            </th>
            <th>商品</th>
            <th>商家</th>
            <th>价格</th>
        </tr>
        <tr>
            <td>
                <input type="checkbox" name="check" class="ck" />
            </td>
            <td>小米手机</td>
            <td>小米</td>
            <td>￥1999</td>
        </tr>
        <tr>
            <td>
                <input type="checkbox" name="check" class="ck" />
            </td>
            <td>小米净水器</td>
            <td>小米</td>
            <td>￥4999</td>
        </tr>
        <tr>
            <td>
                <input type="checkbox" name="check" class="ck" />
            </td>
            <td>小米电视</td>
            <td>小米</td>
            <td>￥5999</td>
        </tr>
    </table>