看書：<input type="checkbox" name="checkbox" value=1><br>
寫字：<input type="checkbox" name="checkbox"value=2><br>
玩遊戲：<input type="checkbox" name="checkbox"value=4><br>
<button onclick="checkboxed('checkbox')">全選</button>
<button onclick="uncheckboxed('checkbox')"
 
>取消全選</button>

function checkboxed(objName){
    var objNameList=document.getElementsByName(objName);    

    if(null!=objNameList){
        alert("全選操作");
        for(var i=0;i<objNameList.length;i++){
            objNameList[i].checked="checked";
        }
    }
}

function uncheckboxed
 
(objName){
    var objNameList=document.getElementsByName(objName);    

    if(null!=objNameList){
        alert("取消全選操作");
        for(var i=0;i<objNameList.length;i++){
            objNameList[i].checked="";
        }
    }
}