js checkbox

//复选框全选
var oCheckBox ={
    _check_all: function(obj){
        if("all" == obj.name){
            if(obj.checked){
                $("#days input:checkbox").each(function(){
                    this.checked = true;
                });
            }else{
                 $("#days input:checkbox").each(function(){
                    this.checked = false;
                });
            }
        }else{
            var oAll = document.getElementById("checkall");
            if(obj.checked){
                var allDays = document.getElementById("days").childNodes;
                for (var i=0; i < allDays.length; i++)
                {
                    if((allDays[i].type == "checkbox") &&  !allDays[i].checked){
                         oAll.checked = false;
                         return;
                    }
                }
                oAll.checked = true;
            }else{
                oAll.checked = false;
            }
        }
    },
    _init_checkbox:function(){
        $("#days input:checkbox").each(function(){
            $(this).attr("checked", false);
        });
        $("#checkall").attr("checked", false);
    }
}