var reg = /^\w{3,10}$/;
var reg2 = /^.{6,20}$/;
var userName  = document.getElementById('username');
var password  = document.getElementById('password');
var password2 = document.getElementById('password-2'); 

if (!reg.test(userName.value)) {
   alert(userName.value+"不符合规定的用户名");
   return false;
}
if (!reg2.test(password.value))   { 
   alert(password.value+"不符合规定的密码");
   return false;
}
if (!(password.value === password2.value))  {
   alert(password2.value+"两次密码不一致");
   return false;
}
return true;

}