mirror: A fast canonicalisation utility for stable object equality
chore: code down to 535B
Marais Rossouw
(Jun 25, 2026, 4:12 PM +1000)
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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 type = typeof input;
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if (type !== 'object') {
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if (type === 'number') return input - input === 0 ? 'n' + input : 'L';
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if (type === 'string') return 's' + input;
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if (type === 'bigint') return 'n' + input;
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if (type === 'boolean') return input ? 'T' : 'F';
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// functions, symbols, undefined are dropped and treated as identity equal.
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let out: string, i = 0, keys: any, tmp: any;
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if ((tmp = typeof input) !== '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 (tmp === 'boolean') return input ? 'T' : 'F';
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return;
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}
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// Arrays are the most common container, so settle them before the rarer
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// Date/RegExp leaves to keep the hot path short.
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let is_arr = Array.isArray(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 (typeof input !== 'object' || input === null) return walk(input, seen);
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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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let ref: any = seen.indexOf(input);
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if (~ref) return '~' + (ref + 1);
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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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let out: string, i = 0, keys: any, tmp: any;
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if (is_arr) {
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for (
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out = 'a';
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out = 'e';
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for (let value of input) out += (tmp = walk(value, seen)) === undefined ? 'L' : tmp;
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} else if (input instanceof Map) {
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out = 'o';
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if (input.size > 1) {
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for (keys = [...input.keys()].sort(); i < keys.length; i++) {
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(tmp = walk(input.get(keys[i]), seen)) !== undefined && (out += keys[i] + tmp);
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}
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} else {
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for (keys of input) {
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(tmp = walk(keys[1], seen)) !== undefined && (out += keys[0] + tmp);
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}
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keys = [...input.keys()];
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if (keys.length > 1) keys.sort();
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for (out = 'o'; i < keys.length; i++) {
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if ((tmp = walk(input.get(keys[i]), seen)) !== undefined) out += keys[i] + tmp;
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}
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} // Plain objects, class instances and null-prototype objects have no
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// `Symbol.toStringTag`. Typed arrays (and other ArrayBuffer views) do, but
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// JSON treats them as index-keyed objects, so we walk their keys the same way.
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// Other exotic builtins (Promise, WeakMap, ArrayBuffer) fall through to the throw.
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else if (input[Symbol.toStringTag] === undefined || ArrayBuffer.isView(input)) {
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out = 'o';
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} else if (input[Symbol.toStringTag] === undefined || ArrayBuffer.isView(input)) {
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keys = Object.keys(input);
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if (keys.length > 1) keys.sort();
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for (; i < keys.length; i++) {
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for (out = 'o'; i < keys.length; i++) {
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if ((tmp = walk(input[keys[i]], seen)) !== undefined) out += keys[i] + tmp;
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}
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} else {
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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 571B minified and gzipped, with zero
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- 🪶 **Tiny.** Around 535B minified and gzipped, with zero
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[dependencies](https://npm.anvaka.com/#/view/2d/object-identity/).
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## ⚙️ Install