function selectAllCheckBox(parentid) {            var PID = document.getElementById(parentid);            var cb = PID.getElementsByTagName("input");            for(var i=0;i<cb.length;i++){                if(cb[i].type == "checkbox"){                    cb[i].checked = "checked";                }            }        }

<div id = "awardall-frame-down">　　<button id = "selectallbtn" class="selectallbtn" onclick="selectAllCheckBox(‘awardall-frame-down‘)">全选</button>　　<input type="checkbox" name="area_id" value="Car">一区</input>　　<input type="checkbox" name="area_id" value="Car">二区</input>　　<input type="checkbox" name="area_id" value="Car">三区</input>　　<input type="checkbox" name="area_id" value="Car">四区</input>　　<input type="checkbox" name="area_id" value="Car">五区</input>　　<input type="checkbox" name="area_id" value="Car">六区</input>　　<input type="checkbox" name="area_id" value="Car">七区</input>　　<input type="checkbox" name="area_id" value="Car">八区</input></div>