See it with type checking at https://www.typescriptlang.org/play?#code/FAFwngDgpgBAggJwQQzAZwPIDMCiyDGAFgAoID20C4APACoB8MAvDAN7AycwDapFUVMDACWAOxgBrKGDJYYtALoAueElR1e5SuAX0A3MAC+wYFgCuo-CGFlxWYVAA2AE0QI0tMhgBGAKzR0MFAAHiBQos5obIb0ABTISGgqbqiYuAQkWgI0DACUyWpgdIzsXDD4tmggMAhQICq03ArMPAoGZT6+UFYAdOEgCA5o8Ym5PVhkCHhEsbHcUmAANDAAbsiOZlBoCrnMJRxlXLFrG…

animal-legs.ts

type ArraysOfEachProperty<T> = {
    [Property in keyof T]: Array<T[Property]>;
}

function fieldArrsToObjs<T extends {}>(arrs: ArraysOfEachProperty<T>): Array<T> {
  const ret: T[] = [];
  Object.entries(arrs).forEach(([key, values]) => {
    (values as unknown[]).forEach((value, idx) => {
      if (!ret[idx]) {
        // @ts-expect-error
        ret[idx] = { [key]: value };
      } else {
        // @ts-expect-error
        ret[idx][key] = value;
      }
    });
  });
  return ret;
}

/**
 * Inferred type of legCounts:
 *   Array<{ animal: string, legs: number }>
 */
const legCounts = fieldArrsToObjs({
    animal: ["dog", "cat", "bird"],
    legs: [4, 4, 2],
});