npm install -g json-diff2

json-diff2 a.json b.json

% json-diff2 --help
Usage: json-diff2 [-vjCk] [-p DECIMALS] first.json second.json

Arguments:
  first.json                Old file
  second.json               New file

General options:
  -v, --verbose             Output progress info
  -C, --[no-]color          Colored output
  -j, --raw-json            Display raw JSON encoding of the diff
  -k, --keys-only           Compare only the keys, ignore the differences in values
  -p, --precision DECIMALS  Use DECIMALS for number comparisons (object values only)
  -h, --help                Display this usage information

var jsonDiff = require('json-diff2')

console.log(jsonDiff.diffString({ foo: 'bar' }, { foo: 'baz' }));

// Output:
//  {
// -  foo: "bar"
// +  foo: "baz"
//  }

console.log(jsonDiff.diff({ foo: 'bar' }, { foo: 'baz' }));

// Output:
// { foo: { __old: 'bar', __new: 'baz' } }

import { diffString, diff } from 'json-diff2';

console.log(diffString({ foo: 'bar' }, { foo: 'baz' }));
console.log(diff({ foo: 'bar' }, { foo: 'baz' }));

npm test

npm run-script cov

colorize
  ✓ should return ' <value>' for a scalar value
  ✓ should return '-<old value>', '+<new value>' for a scalar diff
  ✓ should return '-<removed key>: <removed value>' for an object diff with a removed key
  ✓ should return '+<added key>: <added value>' for an object diff with an added key
  ✓ should return '+<added key>: <added stringified value>' for an object diff with an added key and a non-scalar value
  ✓ should return ' <modified key>: <colorized diff>' for an object diff with a modified key
  ✓ should return '+<inserted item>' for an array diff
  ✓ should return '-<deleted item>' for an array diff

diff
  with simple scalar values
    ✓ should return undefined for two identical numbers
    ✓ should return undefined for two identical strings
    ✓ should return { __old: <old value>, __new: <new value> } object for two different numbers
  with objects
    ✓ should return undefined for two objects with identical contents
    ✓ should return undefined for two object hierarchies with identical contents
    ✓ should return { <key>__deleted: <old value> } when the second object is missing a key
    ✓ should return { <key>__added: <new value> } when the first object is missing a key
    ✓ should return { <key>: { __old: <old value>, __new: <new value> } } for two objects with diffent scalar values for a key
    ✓ should return { <key>: <diff> } with a recursive diff for two objects with diffent values for a key
  with arrays of scalars
    ✓ should return undefined for two arrays with identical contents
    ✓ should return [..., ['-', <removed item>], ...] for two arrays when the second array is missing a value
    ✓ should return [..., ['+', <added item>], ...] for two arrays when the second one has an extra value
    ✓ should return [..., ['+', <added item>]] for two arrays when the second one has an extra value at the end (edge case test)
  with arrays of objects
    ✓ should return undefined for two arrays with identical contents
    ✓ should return [..., ['-', <removed item>], ...] for two arrays when the second array is missing a value
    ✓ should return [..., ['+', <added item>], ...] for two arrays when the second array has an extra value
    ✓ should return [..., ['~', <diff>], ...] for two arrays when an item has been modified (note: involves a crazy heuristic)

✔ 25 tests complete (12ms)