[рони]

Neznajka,

let arrayMain = [
  {
    order: 234,
    Dat: '23-11',
    firma: 156,
    director: 45,
    zakaz: [
      { produkt: 34, sum: 5 },
      { produkt: 17, sum: 1 },
      { produkt: 24, sum: 3 },
      { produkt: 19, sum: 5 }
    ]
  },
  {
    order: 235,
    Dat: '24-11',
    firma: 368,
    director: 12,
    zakaz: [
      { produkt: 17, sum: 2 },
      { produkt: 24, sum: 4 },
      { produkt: 34, sum: 2 }
    ]
  },
  {
    order: 236,
    Dat: '25-11',
    firma: 213,
    director: 96,
    zakaz: [
      { produkt: 24, sum: 7 },
      { produkt: 34, sum: 2 }
    ]
  }
];
let slovarFirm = [
  { kod: 156, name: 'Ямал-сервис' },
  { kod: 213, name: 'Рассвет' },
  { kod: 368, name: 'ЭлектроСила' }
];
let slovarPers = [
  { kod: 12, name: 'Иванов' },
  { kod: 45, name: 'Петров' },
  { kod: 96, name: 'Сидоров' }
];
let slovarProd = [
  { kod: 17, name: 'Бумага' },
  { kod: 19, name: 'Маркеры' },
  { kod: 24, name: 'Скрепки' },
  { kod: 34, name: 'Карандаши' }
];
const createObj = (arr) =>
  arr.reduce(function (obj, el) {
    obj[el.kod] = el.name;
    return obj;
  }, {});
slovarFirm = createObj(slovarFirm);
slovarPers = createObj(slovarPers);
slovarProd = createObj(slovarProd);
arrayMain = arrayMain.map(function (ob) {
  ob.firma = slovarFirm[ob.firma];
  ob.director = slovarPers[ob.director];
  ob.zakaz.forEach(function (el) {
    el.produkt = slovarProd[el.produkt];
  });
  return ob;
});
console.log(arrayMain);