JS判断表单输入是否为空(示例代码)

//去掉输入字符串两边的空格

function trim(s) {   
   var count = s.length;   
   var st    = 0;       // start   
   var end   = count-1; // end   

   if (s == "") return s;   
   while (st < count) {   
     if (s.charAt(st) == " ")   
       st ++;   
     else  
       break;   
   }   
   while (end > st) {   
     if (s.charAt(end) == " ")   
       end --;   
     else  
       break;   
   }   
   return s.substring(st,end + 1);   
 }

<form action="testnew.html" name="form1">   

  username: <input type="text" name="name">   

  password: <input type="password" name="pwd">   <br>   

  <input type="submit" value="提交" onclick="isEmpty()">   

</form>

function isEmpty(){   
    //form1是form中的name属性   
    var _form = document.form1;   

    if(trim(_form.name.value)==""){   
        alert("用户名不能为空!");           
        return false;   
    }   
    if(trim(_form.pwd.value)==""){   
        alert("密码不能为空!");          
        return false;   
    }  

    return true;

}