std/assert/equal.ts

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

type KeyedCollection = Set<unknown> | Map<unknown, unknown>;
function isKeyedCollection(x: unknown): x is KeyedCollection {
  return x instanceof Set || x instanceof Map;
}

function constructorsEqual(a: object, b: object) {
  return a.constructor === b.constructor ||
    a.constructor === Object && !b.constructor ||
    !a.constructor && b.constructor === Object;
}

/**
 * Deep equality comparison used in assertions.
 *
 * @param c The actual value
 * @param d The expected value
 * @returns `true` if the values are deeply equal, `false` otherwise
 *
 * @example Usage
 * ```ts
 * import { equal } from "@std/assert/equal";
 *
 * equal({ foo: "bar" }, { foo: "bar" }); // Returns `true`
 * equal({ foo: "bar" }, { foo: "baz" }); // Returns `false
 * ```
 */
export function equal(c: unknown, d: unknown): boolean {
  const seen = new Map();
  return (function compare(a: unknown, b: unknown): boolean {
    // Have to render RegExp & Date for string comparison
    // unless it's mistreated as object
    if (
      a &&
      b &&
      ((a instanceof RegExp && b instanceof RegExp) ||
        (a instanceof URL && b instanceof URL))
    ) {
      return String(a) === String(b);
    }
    if (a instanceof Date && b instanceof Date) {
      const aTime = a.getTime();
      const bTime = b.getTime();
      // Check for NaN equality manually since NaN is not
      // equal to itself.
      if (Number.isNaN(aTime) && Number.isNaN(bTime)) {
        return true;
      }
      return aTime === bTime;
    }
    if (typeof a === "number" && typeof b === "number") {
      return Number.isNaN(a) && Number.isNaN(b) || a === b;
    }
    if (Object.is(a, b)) {
      return true;
    }
    if (a && typeof a === "object" && b && typeof b === "object") {
      if (a && b && !constructorsEqual(a, b)) {
        return false;
      }
      if (a instanceof WeakMap || b instanceof WeakMap) {
        if (!(a instanceof WeakMap && b instanceof WeakMap)) return false;
        throw new TypeError("cannot compare WeakMap instances");
      }
      if (a instanceof WeakSet || b instanceof WeakSet) {
        if (!(a instanceof WeakSet && b instanceof WeakSet)) return false;
        throw new TypeError("cannot compare WeakSet instances");
      }
      if (a instanceof WeakRef || b instanceof WeakRef) {
        if (!(a instanceof WeakRef && b instanceof WeakRef)) return false;
        return compare(a.deref(), b.deref());
      }
      if (seen.get(a) === b) {
        return true;
      }
      if (Object.keys(a).length !== Object.keys(b).length) {
        return false;
      }
      seen.set(a, b);
      if (isKeyedCollection(a) && isKeyedCollection(b)) {
        if (a.size !== b.size) {
          return false;
        }

        const aKeys = [...a.keys()];
        const primitiveKeysFastPath = aKeys.every((k) => {
          return typeof k === "string" ||
            typeof k === "number" ||
            typeof k === "boolean" ||
            typeof k === "bigint" ||
            typeof k === "symbol" ||
            k == null;
        });
        if (primitiveKeysFastPath) {
          if (a instanceof Set) {
            return a.symmetricDifference(b).size === 0;
          }

          for (const key of aKeys) {
            if (
              !b.has(key) ||
              !compare(a.get(key), (b as Map<unknown, unknown>).get(key))
            ) {
              return false;
            }
          }
          return true;
        }

        let unmatchedEntries = a.size;

        for (const [aKey, aValue] of a.entries()) {
          for (const [bKey, bValue] of b.entries()) {
            /* Given that Map keys can be references, we need
             * to ensure that they are also deeply equal */

            if (!compare(aKey, bKey)) continue;

            if (
              (aKey === aValue && bKey === bValue) ||
              (compare(aValue, bValue))
            ) {
              unmatchedEntries--;
              break;
            }
          }
        }

        return unmatchedEntries === 0;
      }
      const merged = { ...a, ...b };
      for (
        const key of [
          ...Object.getOwnPropertyNames(merged),
          ...Object.getOwnPropertySymbols(merged),
        ]
      ) {
        type Key = keyof typeof merged;
        if (!compare(a && a[key as Key], b && b[key as Key])) {
          return false;
        }
        if (((key in a) && (!(key in b))) || ((key in b) && (!(key in a)))) {
          return false;
        }
      }
      return true;
    }
    return false;
  })(c, d);
}