Makes using arrays that you have zero control over easier to reference values.

dictionaries.js

var userPreferencesDict = [
  'favoriteFood',
  'favoriteColor',
  'favoriteNumber',
];

var userPreferences = [
  'pizza',
  'seafoam green',
  '42'
];

console.log('\n-- Dictionary 1 --------------');
function dictionary (keys, values) {
  return keys.reduce((result, key, index) => {
    result[key] = values[index];
    return result;
  }, {});
}

const preferences1 = dictionary(userPreferencesDict, userPreferences);
console.log('=> favoriteFood', preferences1.favoriteFood);
console.log('=> favoriteColor', preferences1.favoriteColor);
console.log('=> favoriteNumber', preferences1.favoriteNumber);


console.log('\n-- Dictionary 2 --------------');
function Dictionary2 (keys, values) {
  this._keys = keys;
  this._values = values;

  this.get = (key) => {
    const index = this._keys.indexOf(key);
    return this._values[index];
  };

  return this;
}

const preferences2 = new Dictionary2(userPreferencesDict, userPreferences);
console.log('=> favoriteFood', preferences2.get('favoriteFood'));
console.log('=> favoriteColor', preferences2.get('favoriteColor'));
console.log('=> favoriteNumber', preferences2.get('favoriteNumber'));


console.log('\n-- Dictionary 3 --------------');
function Dictionary3 (dict, array) {
  return new Proxy([dict, array], {
    get ([keys, values], key) {
      const index = keys.indexOf(key);
      return values[index];
    }
  });
}

const preferences3 = new Dictionary3(userPreferencesDict, userPreferences);
console.log('=> favoriteFood', preferences3.favoriteFood);
console.log('=> favoriteColor', preferences3.favoriteColor);
console.log('=> favoriteNumber', preferences3.favoriteNumber);

Neat!