JS——全选与全不选

1、每个子input标签都需要进行判断
2、使用开闭原则，一旦满足条件就改变默认值
3、在给主input标签注册事件时，要求主input标签的checked值赋值给子标签
<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        .wrap {
             300px;
            margin: 100px auto 0;
        }

        table {
            border-collapse: collapse;
            border-spacing: 0;
            border: 1px solid #c0c0c0;
             300px;
        }

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

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

        td {
            font: 14px "微软雅黑";
        }

        tbody tr {
            background-color: #f0f0f0;
        }

            tbody tr:hover {
                cursor: pointer;
                background-color: #fafafa;
            }
    </style>
</head>
<body>
    <div class="wrap">
        <table>
            <thead>
                <tr>
                    <th>
                        <input type="checkbox" id="theadInp" />
                    </th>
                    <th>菜名</th>
                    <th>饭店</th>
                </tr>
            </thead>
            <tbody id="tbody">
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>地三鲜</td>
                    <td>田老师</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>西红柿鸡蛋</td>
                    <td>田老师</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>醋溜土豆丝</td>
                    <td>田老师</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>萝卜干炒黄豆儿</td>
                    <td>田老师</td>
                </tr>
            </tbody>
        </table>
    </div>
    <script>
        var inp = document.getElementById("theadInp");
        var tbody = document.getElementById("tbody");
        var inps = tbody.getElementsByTagName("input");
        //给表头的input标签注册事件
        inp.onclick = function () {
            for (var i = 0; i < inps.length; i++) {
                inps[i].checked = this.checked;
            }
        }
        //给tbody中的input标签注册事件
        for (var i = 0; i < inps.length; i++) {
            inps[i].onclick = function () {
                var bool = true;
                for (var i = 0; i < inps.length; i++) {
                    if (inps[i].checked === false) {
                        bool = false;
                    }
                }
                inp.checked = bool;
            }
        }
    </script>
</body>
</html>