Small javascript snippet that asks you the capital of an European country throught a prompt and says if you answered correctly or not every time it's executed. It's in Spanish, traductions welcome. It uses a Key-Value structure to store the countries and its capitals, respectively, includes a null check and LoWeR-uPpEr case support.

europeancountries.js

var capitalList = [
{"K":"Albania","V":"Tirana"},
{"K":"Alemania","V":"Berlín"},
{"K":"Andorra","V":"Andorra la Vella"},
{"K":"Armenia","V":"Ereván"},
{"K":"Austria","V":"Viena"},
{"K":"azerbaiyán","V":"bakú"},
{"K":"Bélgica","V":"Bruselas"},
{"K":"Bielorrusia","V":"Minsk"},
{"K":"Bosnia y Herzegovina","V":"Sarajevo"},
{"K":"Bulgaria","V":"Sofía"},
{"K":"República Checa","V":"Praga"},
{"K":"Croacia","V":"Zagreb"},
{"K":"Dinamarca","V":"Copenhague"},
{"K":"Eslovaquia","V":"Bratislava"},
{"K":"Eslovenia","V":"Liubliana"},
{"K":"España","V":"Madrid"},
{"K":"Estonia","V":"Tallín"},
{"K":"Finlandia","V":"Helsinki"},
{"K":"Francia","V":"París"},
{"K":"Georgia","V":"Tiflis"},
{"K":"Grecia","V":"Atenas"},
{"K":"Hungría","V":"Budapest"},
{"K":"Irlanda","V":"Dublín"},
{"K":"Islandia","V":"Reikiavik"},
{"K":"Italia","V":"Roma"},
{"K":"Letonia","V":"Riga"},
{"K":"Liechtenstein","V":"Vaduz"},
{"K":"Lituania","V":"Vilna"},
{"K":"Luxemburgo","V":"Luxemburgo"},
{"K":"República de Macedonia","V":"Skopje"},
{"K":"Malta","V":"La Valeta"},
{"K":"Moldavia","V":"Chisinau"},
{"K":"Mónaco","V":"Mónaco"},
{"K":"Montenegro","V":"Podgorica"},
{"K":"Noruega","V":"Oslo"},
{"K":"Países Bajos","V":"Amsterdam"},
{"K":"Polonia","V":"Varsovia"},
{"K":"Portugal","V":"Lisboa"},
{"K":"Reino Unido","V":"Londres"},
{"K":"Rumania","V":"Bucarest"},
{"K":"Rusia","V":"Moscú"},
{"K":"San Marino","V":"Ciudad de San Marino"},
{"K":"Serbia","V":"Belgrado"},
{"K":"Suecia","V":"Estocolmo"},
{"K":"Suiza","V":"Berna"},
{"K":"Ucrania","V":"Kiev"},
{"K":"Vaticano","V":"Ciudad del Vaticano"}
];
var randomCountryObject = capitalList[Math.floor(Math.random() * capitalList.length)];
var answer = prompt("Dí la capital de " + randomCountryObject.K);
if(!answer){
    console.log("¡No contestaste weeeey!");
} else if(answer.toLowerCase() == randomCountryObject.V.toLowerCase()) {
    console.log("¡Coooooorrectoooo!");
} else {
    console.log("¡Incorreeeeectooo! La respuesta era " + randomCountryObject.V);
}