mirror: A fast canonicalisation utility for stable object equality
fix: prevent stack overflow on self-referential toJSON
Marais Rossouw
(Jun 30, 2026, 8:57 PM +1000)
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lib/mod.test.ts
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lib/mod.test.ts
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assertEquals(identify(o), identify({ a: 1 }));
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});
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Deno.test('toJSON :: result cycling back to the original does not overflow', () => {
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const fresh: any = {};
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fresh.toJSON = () => ({ wrap: fresh });
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const stable: any = {};
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const wrapper = { wrap: stable };
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stable.toJSON = () => wrapper;
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assertEquals(identify(fresh), identify(fresh));
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assertEquals(identify(fresh), identify(stable));
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});
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Deno.test('toJSON :: result resolving to an ancestor closes the cycle', () => {
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const getter: any = {
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get g() {
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return { toJSON: () => getter };
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},
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};
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assert(identify(getter));
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assertEquals(identify(getter), identify(getter));
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const parent: any = {};
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const child: any = { toJSON: () => parent };
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parent.child = child;
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assert(identify(parent));
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assertEquals(identify(parent), identify(parent));
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const root: any = {};
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const mid: any = {};
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root.mid = mid;
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mid.leaf = { toJSON: () => root };
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assert(identify(root));
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assertEquals(identify(root), identify(root));
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});
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Deno.test('toJSON :: ancestor cycles resolve through every container', () => {
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const viaSet: any = { s: new Set() };
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viaSet.s.add({ toJSON: () => viaSet });
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const viaMap: any = { m: new Map() };
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viaMap.m.set('k', { toJSON: () => viaMap });
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const viaArray: any = { arr: [] as unknown[] };
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viaArray.arr.push({ toJSON: () => viaArray });
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assertEquals(identify(viaSet), identify(viaSet));
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assertEquals(identify(viaMap), identify(viaMap));
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assertEquals(identify(viaArray), identify(viaArray));
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});
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Deno.test('toJSON :: array and mutual results still resolve cycles', () => {
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const arr: any = {};
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arr.toJSON = () => [arr];
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assertEquals(identify(arr), identify(arr));
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const a: any = {};
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const b: any = {};
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a.toJSON = () => ({ b });
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b.toJSON = () => ({ a });
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assertEquals(identify(a), identify(a));
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assertEquals(identify(b), identify(b));
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});
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// ~> Dates & RegExps
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Deno.test('dates :: equal instants match, different instants differ', () => {
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lib/mod.ts
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lib/mod.ts
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function walk(input: any, seen: any[]): string | undefined {
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if (input === null) return 'L';
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let out: string, i = 0, keys: any, tmp: any;
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let out: string, i = 0, keys: any = input, tmp: any = typeof input;
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if ((tmp = typeof input) !== 'object') {
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if (tmp !== 'object') {
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if (tmp === 'number') return input - input === 0 ? 'n' + input : 'L';
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if (tmp === 'string') return 's' + input;
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if (tmp === 'bigint') return 'n' + input;
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if (!is_arr) {
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if (input instanceof Date) return 'd' + +input;
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if (input instanceof RegExp) return 'r' + input.source + input.flags;
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if (typeof input.toJSON === 'function' && !ArrayBuffer.isView(input)) {
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input = input.toJSON();
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if (input === null) return 'L';
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if (typeof input !== 'object') return walk(input, seen);
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is_arr = Array.isArray(input);
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}
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}
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tmp = seen.indexOf(input);
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if (~tmp) return '~' + (tmp + 1);
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seen.push(input);
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if (typeof input.toJSON === 'function' && !ArrayBuffer.isView(input)) {
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input = input.toJSON();
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if (input === null || typeof input !== 'object') return walk(input, seen);
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tmp = seen.indexOf(input);
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if (~tmp) return '~' + (tmp + 1);
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is_arr = Array.isArray(input);
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}
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seen.push(keys);
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if (is_arr) {
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for (
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readme.md
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readme.md
···
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- 🧬 **Canonical.** The same shape always produces the same id.
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- 🌀 **Deep and cycle-safe.** Handles nested objects, arrays, sets, maps, and circular references.
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- 🏎 **Fast.** See the [benchmarks](#-benchmark).
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- 🪶 **Tiny.** Around 535B minified and gzipped, with zero
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- 🪶 **Tiny.** Around 543B minified and gzipped, with zero
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[dependencies](https://npm.anvaka.com/#/view/2d/object-identity/).
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## ⚙️ Install