javascript checkbox全选和反选的简单实现

function tempUser(val){ 
   $("input[name='userid']").each(function() {  
     this.checked = val;  
  }); 
} 

<input type='checkbox' onclick="tempUser(this.checked)" /> 
<input type='checkbox' name="userid" /> 
<input type='checkbox' name="userid" /> 
<input type='checkbox' name="userid" /> 
<input type='checkbox' name="userid" /> 
<input type='checkbox' name="userid" /> 
<input type='checkbox' name="userid" /> 
<input type='checkbox' name="userid" />