全选，反选

<section class="order-list" id="pagination">
    <ul  id="p1" class=" _current" >
      
        <li class="">
            <input type="checkbox" onclick="selectAll()">
            <label>李四</label>
            <span>799688123@qq.com</span>
            <a>详情</a>
        </li>
        <li class="">
            <input type="checkbox" onclick="selectAll()">
            <label>王武</label>
            <span>799688123@qq.com</span>
            <a>详情</a>
        </li>
    </ul>
    <ul id="p2" class=" " style="display: none;">
        <li class="">
            <input type="checkbox" onclick="selectAll()">
            <label>张三</label>
            <span>799688123@qq.com</span>
            <a>详情</a>
        </li>
        <li class="">
            <input type="checkbox" onclick="selectAll()">
            <label>李四</label>
            <span>799688123@qq.com</span>
            <a>详情</a>
        </li>
    </ul>
    <div class="all-send">
        <input type="checkbox" onclick="checkAll(this)" id="all">全选
        <a>发送</a>
    </div>
</section>

//全选，取消全选
    $("#checkall").click(
        function(){
            if(this.checked){
                $("input[name='user']").prop('checked', true);

            }else{
                $("input[name='user']").removeAttr("checked");
            }
        }
    );

function checkAll(obj) {
    //alert(obj.checked);
    //获取name=box的复选框
    var userids = $(".order-list li input");
    //alert(userids.length);
    for (var i = 0; i < userids.length; i++) {
        userids[i].checked = obj.checked;
    }
}

function selectAll() {
    //获取name=box的复选框
    var userids = $(".order-list li input");
    var count = 0;
    //遍历所有的复选框
    for (var i = 0; i < userids.length; i++) {
        if (userids[i].checked) {
            count++;
        }
    }
    //选中复选框的个数==获取复选框的个数
    if (count == userids.length) {
        //设置id为all复选框选中
        document.getElementById("all").checked = true;
    } else {
        //设置id为all复选框不选中
        document.getElementById("all").checked = false;
    }

}