Fastest™ JSON deep clone in JavaScript

fast-json-clone is a tiny library to clone JSON values in pure JavaScript focusing on the speed. According to the benchmark, this package seems the fastest among several deep-clone implementations.

import * as assert from 'assert';
import cloneJSON from 'fast-json-clone';

const value = { str: 'hello', num: 42, array: [true, null], object: { str: 'hello', bool: true, } };

const cloned = cloneJSON(value);

assert.deepStrictEqual(value, cloned);
assert.notStrictEqual(value, cloned);
assert.notStrictEqual(value.array, cloned.array);
assert.notStrictEqual(value.object, cloned.object);

Installation

Copy the source directly

This package is licensed with CC0-1.0. Directly copy index.ts to your project.

npm

Install via npm package manager.

npm install --save fast-json-clone

jsr

Install via JSR package registry.

# npm
npx jsr add @rhy/fast-json-clone

# deno
deno add @rhy/fast-json-clone

API

This package exports a single function cloneJSON.

cloneJSON(x: JsonValue): JsonValue;

This function clones the given JSON value and returns it. There are some invariants for the parameter:

• The parameter must not contain circles as JSON does not allow it. This function will cause infinite loop for such values by design.
• The parameter must contain JSON values only. Other values like Date, Regexp, Map, Set, Buffer, ... are not allowed.

Benchmark

Here is the benchmark result with large (1.2MB) JSON value. This package is the fastest among the implementations. Please see the benchmark directory for more details and other results.

Naive deep clone                x 269 ops/sec ±0.33% (90 runs sampled)
JSON serialize/deserialize      x 144 ops/sec ±0.97% (82 runs sampled)
Native structuredClone          x 156 ops/sec ±0.44% (79 runs sampled)
structuredClone polyfill        x 156 ops/sec ±0.31% (80 runs sampled)
lodash.clonedeep                x 169 ops/sec ±2.22% (82 runs sampled)
clone-deep                      x 239 ops/sec ±0.62% (87 runs sampled)
rfdc (default)                  x 558 ops/sec ±0.31% (94 runs sampled)
rfdc (proto)                    x 624 ops/sec ±0.60% (94 runs sampled)
fastest-json-copy               x 627 ops/sec ±0.36% (94 runs sampled)
fast-json-clone (this package)  x 664 ops/sec ±0.33% (96 runs sampled)

Fastest is fast-json-clone (this package)

FAQ

Why is this package the fastest?

Since this package is optimized for removing non-inline function calls in the hot loop as much as possible. rfdc is implemented with the same strategy.

Then why is this package faster than rfdc?

Since this package provides less functionalities. rfdc provides support for some non-JSON types (Date, Regexp, ...). It increases the number of branches in the hot loop so it causes trade-off in performance.

License

This package is distributed under CC0 1.0 (Public Domain). Feel free to copy and paste the implementation directly to your project without any copyright notice.