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                        /JavaScript进阶篇

hobby[parseInt(j)-1].checked=true; 求问解释

<!DOCTYPE HTML>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=gb2312">
        <title>无标题文档</title>
    </head>

    <body>
        <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<bobby.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;
         }// 任务2
        }

        function checkone(){
            var j=document.getElementById("wb").value;

         for(var i=0;i<hobby.length;i++)// 任务3
          if(parseInt(j) > 6 || parseInt(j) < 1 ){
                    alert("不在此范围内，请重新输入!")
                    // document.write(j);
                }
            }
            var hobby = document.getElementsByName("hobby");
            hobby[parseInt(j)-1].checked=true;
        }

        </script>
    </body>
</html>