var name = document.getElementById('username');
var password = document.getElementById('password');
var password2 = document.getElementById('password-2');
var regexName = /[a-zA-Z0-9]{3,10}/;
var regexPassword = /[\S]{6,20}/;
if (!regexName.test(name.value)){
    alert('ilegal username!');
    return false;
}

if (!regexPassword.test(password.value)){
    alert('ilegal password!');
    return false;
}

if (password.value != password2.value){
    alert('two passwords are not same!')
    return false;
}

return true;