@instantdb/core/__tests__/src/utils/weakHash.test.ts

Instant's core local abstraction

import { expect, test } from 'vitest';
import weakHash from '../../../src/utils/weakHash';

// Skipping this test because it times out in CI.
// It should be run manually any time we make changes to weakHash.
test.skip('no collisions across many integer-varying queries', () => {
  const shapes = [
    (i: number) => ({ users: { $: { where: { id: i } } } }),
    (i: number) => ({ posts: { $: { where: { authorId: i } }, author: {} } }),
    (i: number) => ({
      items: {
        $: {
          where: {
            tag: 'b14fae2f-ce9b-4677-b6a9-6dddd81914d0',
            n: i,
          },
        },
      },
    }),
  ];

  for (const shape of shapes) {
    const hashes = new Set<string>();
    let firstCollisionAt: number | null = null;
    for (let i = 0; i < 50_000; i++) {
      const hash = weakHash(shape(i));
      if (hashes.has(hash)) {
        firstCollisionAt = i;
        break;
      }
      hashes.add(hash);
    }
    expect(firstCollisionAt, `collision at i=${firstCollisionAt}`).toBeNull();
  }
});

test('is stable across object key order and undefined values', () => {
  expect(weakHash({ b: 2, a: 1, c: undefined })).toBe(weakHash({ a: 1, b: 2 }));
});

test('keeps array and top-level undefined explicit', () => {
  expect(weakHash([undefined])).not.toBe(weakHash([]));
  expect(weakHash([undefined])).not.toBe(weakHash([null]));
  expect(weakHash(undefined)).not.toBe(weakHash(null));
});

test('distinguishes objects by their toJSON output', () => {
  expect(weakHash({ $gt: new Date(1) })).not.toBe(
    weakHash({ $gt: new Date(2) }),
  );
  expect(weakHash(new Date(1))).toBe(weakHash(new Date(1).toISOString()));
});

test('handles bigint values without throwing', () => {
  expect(() => weakHash({ id: 123n })).not.toThrow();
  expect(weakHash(123n)).not.toBe(weakHash(123));
  expect(weakHash(123n)).not.toBe(weakHash('123'));
  expect(weakHash(123n)).not.toBe(weakHash('123n'));
});

// Smoke test: pins the output for a known query so any accidental
// regression in the hash function (e.g. changed constants) trips here
// before silently invalidating every existing IndexedDB cache.
test('produces a stable hash for a known query', () => {
  expect(weakHash({ users: { $: { where: { id: 42 } } } })).toBe(
    'c1413dfe29f87b89',
  );
});