Introduction

json-patch-gen is a small, [thoroughly tested] tests library for generating a [JSON Patch] rfc6902 from two JavaScript objects or arrays.

This library has no dependencies. It supports generating patches of arbitrarily nested objects and arrays to any depth.

json-patch-gen does not apply patches. There are several libraries that can perform this for you:

• jsonpatch
• jsonpatch-js
• fast-json-patch
• rfc6902

If you wish to modify an object and then generate a patch from the modifications just performed, [this library] starcounter may work better for you. It uses an observer to achieve this. Json-patch-gen takes a different approach: it recursively compares the two values given.

It appears that rfc6902 can also generate patches. I missed this while researching a solution to this problem. I've not compared the projects. There is room for different approaches to generating patches so I suggest trying both libraries to see which works better for you.

Installation

npm install json-patch-gen --save

or

bower install json-patch-gen

Once installed, the module exports a single function that takes two values to diff.

var diff = require('json-patch-gen');

You can also use this library in the browser by loading with a script tag. A single 'diff' function will be exported to the global scope.

Examples

Here is a simple example repl session:

> var diff = require('json-patch-gen');
undefined

> diff({},{});
[]

> diff([],[1])
[ { op: 'add', path: '/0', value: 1 } ]

> diff({foo: 'bar'}, {foo: 'baz'})
[ { op: 'replace', path: '/foo', value: 'baz' } ]

> diff({foo: 'bar'}, {})
[ { op: 'remove', path: '/foo' } ]

> diff({}, {foo: 'bar'})
[ { op: 'add', path: '/foo', value: 'bar' } ]

> diff({foo: {bar: 'baz'}}, {foo: {bar: 'quux'}})
[ { op: 'replace', path: '/foo/bar', value: 'quux' } ]

> diff([1,2,3], [2,3,4])
[ { op: 'add', path: '/3', value: 4 },
  { op: 'remove', path: '/0' } ]

> diff([{foo: 'bar'},3], [{foo: 'baz'},3,4])
[ { op: 'add', path: '/2', value: 4 },
  { op: 'replace', path: '/0/foo', value: 'baz' } ]

> diff({foo: {bar: [1,2,3]}}, {foo: {bar: [2,3,4]}})
[ { op: 'add', path: '/foo/bar/3', value: 4 },
  { op: 'remove', path: '/foo/bar/0' } ]