(6个name="hobby"的复选项，两个按钮)来区分三种方法的不同---区别getElementByID,getElementsByName,getElem

<form>
          请选择你爱好:<br>
          <input type="checkbox" name="hobby" id="hobby1">  音乐
          <input type="checkbox" name="hobby" id="hobby2">  登山
          <input type="checkbox" name="hobby" id="hobby3">  游泳
          <input type="checkbox" name="hobby" id="hobby4">  阅读
          <input type="checkbox" name="hobby" id="hobby5">  打球
          <input type="checkbox" name="hobby" id="hobby6">  跑步 <br>
          <input type="button" value = "全选" onclick = "checkall();">
          <input type="button" value = "全不选" onclick = "clearall();">
          <p>请输入您要选择爱好的序号，序号为1-6:</p>
          <input id="wb" name="wb" type="text" >
          <input name="ok" type="button" value="确定" onclick = "checkone();">
        </form>
        <script type="text/javascript">
        function checkall(){
            var hobby = document.getElementsByTagName("input");
            for(var i=0; i<hobby.length; i++){
              hobby[i].checked=true;
            }
        }
        
        function clearall(){
            var hobby = document.getElementsByName("hobby");
           for(var i=0; i<hobby.length;i++ ){
               hobby[i].checked=false;
           }
        }
        
        function checkone(){
            var j=document.getElementById("wb").value;
             if(parseInt(j)>6||parseInt(j)<1)
            {
                alert("请输入1-6之间的数字");
            }
            var hobby=document.getElementsByName("hobby");
            hobby[parseInt(j)-1].checked=true;
        }
        </script>