Find card's brand by given card number using it's prefix.

card.js

/*
  Creates a mapping like:
  {
    '2': { # length 2
      '33': 'Card X'
    },
    '1': {  # length 1
      '4': 'Card Y',
    }
  }

  locate by max length prefixes to min length ones.
*/

function map_card_prefixes(cards_table) {
  const mapping = {};

  Object.keys(cards_table).forEach((card_name) => {
    cards_table[card_name].forEach((prefix) => {
      const prefix_by_length = mapping[`${prefix}`.length] || {};
      prefix_by_length[`${prefix}`] = card_name;
      mapping[`${prefix}`.length] = prefix_by_length;
    });
  });

  return mapping;
}


function create_prefix_translator(cards_table) {
  const prefix_mapping = map_card_prefixes(cards_table);
  const max_length = Math.max(...Object.keys(prefix_mapping));
  const empty_object = {};

  function filter_by_length(card_number, length) {
    const current_mapping = prefix_mapping[`${length}`] || empty_object;
    const result = current_mapping[`${card_number}`.substring(0, length)];

    if (length < 2 || result) {
      return result;
    }

    return filter_by_length(card_number, length - 1);
  }

  function find_card_brand(card_number) {
    return filter_by_length(card_number, max_length);
  }

  return find_card_brand;
}


const translator = create_prefix_translator({
  'Visa': [23, 568, 4],
  'Master Card': [45, 56942, 235],
  'Nardcred': [10, 2347, 2],
});


console.assert(translator(234444) === 'Visa', 'Expected Visa');
console.assert(translator(235544) === 'Master Card', 'Expected Master Card');
console.assert(translator(211111) === 'Nardcred', 'Expected Nardcred');
console.assert(translator(5694211) === 'Master Card', 'Expected Master Card');
console.assert(translator(5684211) === 'Visa', 'Expected Visa');