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Deterministic-Object-Hash

A deterministic object hashing algorithm for Node.js and web platform.

The Problem

Using JSON.stringify on two objects that are deeply equal does not lead to the same output string. Instead the keys are ordered in the same order that they were added. This leads to two objects that are deeply equal being hashed to different values.

import { createHash } from "crypto";
import { isEqual } from "lodash";

const obj1: Record<string, string> = {};
obj1['a'] = 'x';
obj1['b'] = 'y';
obj1['c'] = 'z';

const obj2: Record<string, string> = {};
obj2['c'] = 'z';
obj2['b'] = 'y';
obj2['a'] = 'x';

isEqual(obj1, obj2);
// -> true

const string1 = JSON.stringify(obj1);
// -> {"a":"x","b":"y","c":"z"}
const string2 = JSON.stringify(obj2);
// -> {"c":"z","b":"y","a":"x"}

createHash('sha1').update(string1).digest('hex');
// -> ff75fe071d236ce309c15d5636ecaa86c0519ebc
createHash('sha1').update(string2).digest('hex');
// -> 2e53bac865f7be77c8e10cd86d737fbbf259ed37

Usage

Pass a value and receive a deterministic hash of the value.

import deterministicHash from 'deterministic-object-hash';

const objA = { a: 'x', arr: [1,2,3,4], b: 'y' };
const objB = { b: 'y', a: 'x', arr: [1,2,3,4] };

await deterministicHash({
	c: [ objA, objB ],
	b: objA,
	e: objB,
	f: ()=>{ Math.random(); },
	g: Symbol('Unique identity'),
	h: new Error('AHHH')
});
// -> 4c57bcb76498dca7b98ef9747c8f1e7f10c30388

await deterministicHash({
	h: new Error('AHHH'),
	e: objB,
	g: Symbol('Unique identity'),
	b: objA,
	f: ()=>{ Math.random(); },
	c: [ objA, objB ]
});
// -> 4c57bcb76498dca7b98ef9747c8f1e7f10c30388

Settings

A hash algorithm can be passed as the second argument. This takes any value that is valid for webcrypto.subtle.digest. The default is SHA-1.
A digest format can be passed as the third argument. This takes any value that is valid for Hash.digest. The default is hex.

await deterministicHash('value', 'SHA-1');
// -> efede6000ad4e1ff258a38866c71aa351d3c01f6
await deterministicHash('value', 'SHA-256', 'hex');
// -> a0b7821a11db531982044ca5ca2e788e2d749d6b696cd3aa4172342f584f2ee1
await deterministicHash('value', 'SHA-512', 'base64');
// -> 514CuHw/31qqUH2waqaqhKSMvLYH/YdZeRI4QqDBwhKbUk0/3mxhv4NUubXIl5Dm2k0VpU6ZZkmunEb10RngfQ==

Supported Values
String Number
Boolean Function
Plain Objects Symbol
undefined null
Infinity NaN
BigInt Array
Classes/Inheritance Errors
Date RegExp
Map Set
Int8Array Uint8Array
Int16Array Uint16Array
Int32Array Uint32Array
Float32Array Float64Array
BigInt64Array BigUint64Array
Uint8ClampedArray globalThis
ArrayBuffer SharedArrayBuffer

Unsupported Values
WeakMap WeakSet
Atomics DataView
Promises Reflect
Proxy

Due to their nature, WeakSet and WeakMap are not enumerable. As a result there is no way to know what is in a WeakSet/WeakMap unless we are told.

Support

Currently this has only been tested on Node.js 18.x.x. More tests are to come and this section will be updated as I test them.

Contributors

Contributions are welcome. Feel free to create a PR and tag zbauman3.

Past contributors: