var username = document.getElementById('username');
    var pswd = document.getElementById('password');
    var pswd2 = document.getElementById('password-2');
    var usernameRexp = /[0-9a-zA-Z]{3-10}/;
    if(!usernameRexp.test(username.value)){
       alert('用户名格式不正确'); 
       return false;
    }
    if(pswd.length>20||pswd.length<6){
        alert('密码长度应该在6-20位之间');
        return false;
     }
    if(pswd.value!==pswd2.value){
       alert('两次密码不一致');
       return false;
    }
    return true;
}