复选框全选二

复选框全选2
function checkOne(obj){
  if(!obj.checked){
  document.forms[0].selectAllCK.checked = obj.checked; 
  }
  var b = true;
  var arr = document.getElementsByName(obj.name);
  for(var i=0;i<arr.length;i++){
  if(!arr[i].checked){b=false; break;}
  }
  document.forms[0].selectAllCK.checked = b;
}