JSum

Consistent checksum calculation of JSON objects.

Quick start

const JSum = require('jsum')

const obj1 = {foo: [{c: 1}, {d: 2, e: 3}], bar: {a: 2, b: undefined}}
const obj2 = {bar: {b: undefined, a: 2}, foo: [{c: 1}, {e: 3, d: 2}]}

console.log(JSum.digest(obj1, 'SHA256', 'hex')) // 9a08ad6302b1e9e5682c365c8b24c5ca2ea6db5c90b672bc5b579879136dda0c
console.log(JSum.digest(obj2, 'SHA256', 'hex')) // 9a08ad6302b1e9e5682c365c8b24c5ca2ea6db5c90b672bc5b579879136dda0c

Why this module?

My main goal was to create Etags from JSON objects. The most intuitive approach would have been something like:

const crypto = require('crypto')

function checksum (obj) {
  return crypto.createHash('MD5').update(JSON.stringify(myObj)).digest('hex')
}

However, this approach would yield two different results for semantically same JSON objects:

console.log(checksum({"a": 1, "b": 2})) // 608de49a4600dbb5b173492759792e4a
console.log(checksum({"b": 2, "a": 1})) // 9915965eb40d343a8fe26e4e341d1a05

JSum on other hand makes sure that semantically same JSON objects always get the same checksum! Moreover, it provides a good deal of time advantage over some other viable modules*:

Module	Time (ms) to hash a 181 MB JSON file (from memory)
json-hash	81537
json-stable-stringify	12134
JSum	7200
json-checksum	FATAL ERROR: [...] - process out of memory

For this trivial test a huge random JSON file (181 MB) was taken as the base for benchmarking. The listed modules were used to create SHA256 hash of that file. To measure the time, internal console.time(() and console.timeEnd() methods were used. Serious benchmarking is described below.

Benchmarking

You can also run benchmarks to compare performance with similar modules:

npm i --no-save \
  benchmarked \
  fast-json-stable-stringify \
  json-checksum json-hash \
  json-stable-stringify
node benchmark/index.js

Results:

# benchmark/fixtures/medium.json (77986 bytes)
  fast-json-stable-stringify x 1,191 ops/sec ±1.11% (89 runs sampled)
  json-checksum x 406 ops/sec ±2.04% (89 runs sampled)
  json-hash x 148 ops/sec ±2.08% (75 runs sampled)
  json-stable-stringify x 1,051 ops/sec ±2.29% (88 runs sampled)
  jsum x 1,339 ops/sec ±0.77% (93 runs sampled)

  fastest is jsum

# benchmark/fixtures/small.json (456 bytes)
  fast-json-stable-stringify x 116,709 ops/sec ±2.25% (91 runs sampled)
  json-checksum x 36,311 ops/sec ±1.66% (91 runs sampled)
  json-hash x 12,051 ops/sec ±3.62% (77 runs sampled)
  json-stable-stringify x 91,078 ops/sec ±2.08% (89 runs sampled)
  jsum x 116,130 ops/sec ±1.46% (90 runs sampled)

  fastest is jsum