var userName = document.getElementById('username').value, passWord = document.getElementById('password').value, passWord2 = document.getElementById('password-2').value, name = /^[0-9A-Za-z]{3,10}$/, password = /[^]{6,20}/;

if (!name.test(userName)) { alert('用户名必须是3-10位英文字母或数字'); return false; } else if (!password.test(passWord)) { alert('口令必须是6-20位'); return false; } else if (!(passWord === passWord2)) { alert('两次输入口令必须一致'); return false; } else { return true; }
}