Deterministic-Object-Hash

A deterministic object hashing algorithm for Node.js.

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] };

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

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 crypto.createHash. The default is sha1.
A digest format can be passed as the third argument. This takes any value that is valid for Hash.digest. The default is hex.

deterministicHash('value', 'sha1');
// -> efede6000ad4e1ff258a38866c71aa351d3c01f6
deterministicHash('value', 'sha256', 'hex');
// -> a0b7821a11db531982044ca5ca2e788e2d749d6b696cd3aa4172342f584f2ee1
deterministicHash('value', 'sha512', '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 16.3.x. More tests are to come and this section will be updated as I test them.