zustand/vanilla/shallow.js

🐻 Bear necessities for state management in React

'use strict';

const isIterable = (obj) => Symbol.iterator in obj;
const hasIterableEntries = (value) => (
  // HACK: avoid checking entries type
  "entries" in value
);
const compareEntries = (valueA, valueB) => {
  const mapA = valueA instanceof Map ? valueA : new Map(valueA.entries());
  const mapB = valueB instanceof Map ? valueB : new Map(valueB.entries());
  if (mapA.size !== mapB.size) {
    return false;
  }
  for (const [key, value] of mapA) {
    if (!Object.is(value, mapB.get(key))) {
      return false;
    }
  }
  return true;
};
const compareIterables = (valueA, valueB) => {
  const iteratorA = valueA[Symbol.iterator]();
  const iteratorB = valueB[Symbol.iterator]();
  let nextA = iteratorA.next();
  let nextB = iteratorB.next();
  while (!nextA.done && !nextB.done) {
    if (!Object.is(nextA.value, nextB.value)) {
      return false;
    }
    nextA = iteratorA.next();
    nextB = iteratorB.next();
  }
  return !!nextA.done && !!nextB.done;
};
function shallow(valueA, valueB) {
  if (Object.is(valueA, valueB)) {
    return true;
  }
  if (typeof valueA !== "object" || valueA === null || typeof valueB !== "object" || valueB === null) {
    return false;
  }
  if (!isIterable(valueA) || !isIterable(valueB)) {
    return compareEntries(
      { entries: () => Object.entries(valueA) },
      { entries: () => Object.entries(valueB) }
    );
  }
  if (hasIterableEntries(valueA) && hasIterableEntries(valueB)) {
    return compareEntries(valueA, valueB);
  }
  return compareIterables(valueA, valueB);
}

exports.shallow = shallow;