Practice your vietnamese numbers

practiceNumbers.js

var readline = require('readline');

var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

var digitsVietMap = {
  0: 'không',
  1: 'một',
  2: 'hai',
  3: 'ba',
  4: 'bốn',
  5: 'năm',
  6: 'sáu',
  7: 'bảy',
  8: 'tám',
  9: 'chín',
  10: 'mười',
  100: 'trăm',
  1000: 'nghìn'
};

var additionalRules = {
  1: '',
  5: 'lăm',
  0: 'linh',
  10: 'mưoi'
};


function digitInPlace(number, place){
  var numInPlace = 0;
  if (place > number || number > place*10) return false;
  while (place * (numInPlace+1) <= number) numInPlace++;
  return numInPlace;
}

function numberToViet(number, responseSoFar){
  var hundreds, tens, ones, response;
  if (number > 999) return "I don't know that yet.";
  if (!responseSoFar) responseSoFar = '';
  else if (responseSoFar) responseSoFar += ' ';
  debugger;
  if ((hundreds = digitInPlace(number, 100)) !== false) {
    response = digitsVietMap[hundreds] + ' ' + digitsVietMap[100];
    return numberToViet(number - hundreds*100, response);
  }
  else if ((tens = digitInPlace(number, 10)) !== false){
    if (tens == 1) {
      response = '';
    }
    else if (tens == 0) {
      response = additionalRules[tens] + " ";
    }
    else {
      response = digitsVietMap[tens] + " ";
    }
    response += ((tens > 1) ? additionalRules[10] : digitsVietMap[10]);
    return numberToViet(number - tens*10, responseSoFar + response);
  }
  else {
    if (number == 0) return responseSoFar;
    else if (number == 5 && responseSoFar) return responseSoFar + additionalRules[number];
    else return responseSoFar + digitsVietMap[number];
  }
};

var ask = function(question, answer, next){
  rl.question(question + "? ", function(response){
    response = response.trimRight("\n");
    console.log(response);
    if (response == answer) console.log("Đúng!");
    else console.log("Không, " + answer);
    if (typeof next == 'function') next();
  });
};

var askNumber = function(){
  var n, r = Math.random();
  if (r > .6) {
    n = Math.floor(Math.random()*1000);
  } else if (r > .3) {
    n = Math.floor(Math.random()*100);
  } else {
    n = Math.floor(Math.random()*21);
  }
  var viet = numberToViet(n);
  ask(viet, n, askNumber);
};

askNumber();