froebel/equal.mjs

TypeScript utility library

/**
 * Checks if `a` and `b` are structurally equal using the following algorithm:
 *
 * - primitives are compared by value
 * - functions are compared by reference
 * - objects (including arrays) are checked to have the same properties and
 *   their values are compared recursively using the same algorithm
 */
export default function equal(a, b) {
  if (typeof a !== "object" && typeof b !== "object") return a === b;
  if (typeof a === "object" !== (typeof b === "object")) return false;
  if (a === b) return true; // null or ref equality

  if (a === null || b === null) return false;
  if (Array.isArray(a) !== Array.isArray(b)) return false;

  if (Object.keys(a).length !== Object.keys(b).length) {
    return false;
  }

  return Object.entries(a).every(([k, v]) => k in b && equal(v, b[k]));
}