checkbox全选与反选简单代码

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" />