Determine the difference between two iterables, returns {toAdd, toRemove}

diffSets.js

/**
 * @template T
 * @param {Iterable<T>} original
 * @param {Iterable<T>} updated
 */
function diffSets(original, updated) {
  const toRemove = new Set(original);
  const toAdd = new Set();
  // compare which items are new to us
  for (const id of updated) {
    if (toRemove.has(id)) {
      // we have it, so we shouldn't remove it
      toRemove.delete(id);
    } else {
      toAdd.add(id);
    }
  }
  return { toRemove, toAdd };
}

diffSets.ts

function diffSets<T>(original: Iterable<T>, updated: Iterable<T>) {
  const toRemove = new Set(original);
  const toAdd = new Set<T>();
  // compare which items are new to us
  for (const id of updated) {
    if (toRemove.has(id)) {
      // we have it, so we shouldn't remove it
      toRemove.delete(id);
    }
    else {
      toAdd.add(id);
    }
  }
  return { toRemove, toAdd };
}

diffSetsWithData.ts

function diffSetsWithData<T, U>(original: Iterable<[T, U]>, updated: Iterable<[T, U]>) {
  const toRemove = new Map<T, U>(original);
  const toAdd = new Map<T, U>();
  // compare which items are new to us
  for (const [id, data] of updated) {
    if (toRemove.has(id)) {
      // we have it, so we shouldn't remove it
      toRemove.delete(id);
    } else {
      toAdd.set(id, data);
    }
  }
  return { toRemove, toAdd };
}