get difference between array of lines. Which fields are different

index.ts

interface TableRow {
  id: number,
  fa: {
    qty: number
  },
  fd: {
    qty: number
  },
  ka: {
    qty: number
  },
}

const original = [
  {
    id: 23,
    fa: {qty: 2},
    fd: {qty: 2},
    ka: {qty: 2},
  },
  {
    id: 24,
    fa: {qty: 2},
    fd: {qty: 2},
    ka: {qty: 2},
  },
];

const newData = [
  {
    id: 23,
    fa: {qty: 2},
    fd: {qty: 2},
    ka: {qty: 2},
  },
  {
    id: 24,
    fa: {qty: 2},
    fd: {qty: 2},
    ka: {qty: 1},
  },
];

interface Output {
  id: number,
  fa: number,
  fd: number,
  ka: number,
}

const changes: Partial<Output[]> = [];

const objectIs = (a: object, b: object) => JSON.stringify(a) === JSON.stringify(b)

original.forEach((item, index) => {
  const cp = newData[index] as TableRow;

  const obj = {} as Partial<Output>;

  obj.id = item.id;

  for (const key in item) {

    const itemKey = key as keyof Partial<TableRow>

    if (typeof cp[itemKey] === 'object' && typeof item[itemKey] === 'object') {
      if (!objectIs(cp[itemKey] as object, item[itemKey] as object)) {
        obj[itemKey] = ((cp[itemKey] as keyof Pick<TableRow, 'fa' | 'fd' | 'ka'> & number) as any).qty
      }
    }
    else {
      if (cp[itemKey] !== item[itemKey]) {
        obj[itemKey] = cp[itemKey] as any
      }
    }
  }

  changes.push(obj as Output);
});

console.log({ changes });

https://www.typescriptlang.org/play?#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-AHg21kHBeehsHgiAzKBHmWzxiQpKnefjCcSsGTPj8wNSc842WqaOMfRBmE3qPWXVBkHy8zoIMIqCAqL7ZeQDP3W8wANKD8baedpgfCfAwZBlomkjM4AiEanWJI63siL4QNcor6J31z4Qpw1+ADkks5j+QADJ38hT+f19Pr22t73kaz5slKj7jgYRTrnyACEL7cvYfZXtOQElg2wpgP6voAbOg4psuCHSpBSRJEKuFoX4XpRhR+HoYuq7rriwAINoJI7lmhCio+8BvgAPsgPHUPxgm6I+tJfnCsrLhiwjSmqRhQcgVhJCp-AQFg9goLs0G9jRqF0bBRr-gZd4kaRlDkaZ96XrRd7obJSlqeY0iHii6KYtiao-PYnpCuh5I1tKXRSMFiIOPgOBqlg+BuHyJDuRiWK8qFHRAA