js 表单的选择与反选简单操作

    window.onload = function () {
        var firstCb = document.getElementById("firstCb");
        var cbs = document.getElementsByName("cb");


        //全选
        firstCb.onclick = function () {
            for (var i = 0; i <cbs.length ; i++) {
                cbs[i].checked = this.checked;
            }
        }


        document.getElementById("selectAll").onclick = function () {
            for (var i = 0; i <cbs.length ; i++) {
                cbs[i].checked = true;
            }
        }


        document.getElementById("unSelectAll").onclick = function () {
            for (var i = 0; i <cbs.length ; i++) {
                cbs[i].checked = false;
            }
        }

        document.getElementById("selectRev").onclick = function () {
            for (var i = 0; i <cbs.length ; i++) {
                if(cbs[i].checked){
                    cbs[i].checked = false;
                }else if(!cbs[i].checked){
                    cbs[i].checked = true;
                }
            }
        }

    }

<table>
    <caption>学生信息表</caption>
    <tr>
        <th><input type="checkbox" name="cb" id="firstCb"></th>
        <th>编号</th>
        <th>姓名</th>
        <th>性别</th>
        <th>操作</th>
    </tr>

    <tr>
        <td><input type="checkbox"  name="cb" ></td>
        <td>1</td>
        <td>令狐冲</td>
        <td>男</td>
        <td><a href="javascript:void(0);">删除</a></td>
    </tr>

    <tr>
        <td><input type="checkbox"  name="cb" ></td>
        <td>2</td>
        <td>任我行</td>
        <td>男</td>
        <td><a href="javascript:void(0);">删除</a></td>
    </tr>

    <tr>
        <td><input type="checkbox"  name="cb" ></td>
        <td>3</td>
        <td>岳不群</td>
        <td>?</td>
        <td><a href="javascript:void(0);">删除</a></td>
    </tr>

</table>
<div>
    <input type="button" id="selectAll" value="全选">
    <input type="button" id="unSelectAll" value="全不选">
    <input type="button" id="selectRev" value="反选">
</div>