js小功能1：全选全不选

  <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();">
</form>
<script>
   function checkall(){
         var input_all = document.getElementsByName("hobby");
         for(var i=0;i<input_all.length;i++){
                 if(input_all[i].type==='checkbox'){
                      input_all[i].checked=true
                }
           }
 }

function clearall(){
         var input_all = document.getElementsByName("hobby");
         for(var i=0;i<input_all.length;i++){
                 if(input_all[i].type==='checkbox'){
                       input_all[i].checked=false
                }
           }
      }

</script>