全选/反选 js代码

 function   selectAll()
  {
  var collid = document.getElementById("checkAll")
  var coll = document.getElementsByName("check_id")
  if (collid.checked){
     for(var i = 0; i < coll.length; i++)
       coll[i].checked = true;
  }else{
     for(var i = 0; i < coll.length; i++)
       coll[i].checked = false;
  }
  }