JSON-Patch allows you to update a JSON document by sending the changes rather than the whole document.

npm install fast-json-patch
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A leaner and meaner implementation of JSON-Patch. Small footprint. High performance. Also support dual directions! I.e. you can both apply patches and generate patches.

Why you should use JSON-Patch

JSON-Patch (RFC6902) is a new standard format that allows you to update a JSON document by sending the changes rather than the whole document. JSON Patch plays well with the HTTP PATCH verb (method) and REST style programming.

Mark Nottingham has a nice blog about it.


0.5 KB minified and gzipped (1.1 KB minified)




  • Allows you to apply patches on object trees for incoming traffic.
  • Allows you to freely manipulate object trees and then generate patches for outgoing traffic.
  • ES6/7 Object.observe() is used when available.
  • Tested in IE 8-10, Firefox, Chrome and Node.js


  • A /bin directory will be added with minified versions
  • More unit tests

Adding to your project

In a web browser

Include json-patch.js if you want support for applying patches or include json-patch-duplex.js if you also want to generate patches.

In Node.js

Install the current version (and save it as a dependency in package.json):

$ npm install fast-json-patch --save

Call require to get the instance:

var jsonpatch = require('fast-json-patch')

:bulb: Node.js supports native Object.observe in preview release 0.11.x (and only when started with --harmony_observation flag). With stable versions of Node, a shimmed version of Object.observe is used.


Applying patches:

var myobj = { firstName:"Albert", contactDetails: { phoneNumbers: [ ] } };
var patches = [
   {op:"replace", path:"/firstName", value:"Joachim" },
   {op:"add", path:"/lastName", value:"Wester" },
   {op:"add", path:"/contactDetails/phoneNumbers/0", value:{ number:"555-123" }  }
jsonpatch.apply( myobj, patches );
// myobj == { firstName:"Joachim", lastName:"Wester", contactDetails:{ phoneNumbers[ {number:"555-123"} ] } };

Generating patches:

var myobj = { firstName:"Joachim", lastName:"Wester", contactDetails: { phoneNumbers: [ { number:"555-123" }] } };
observer = jsonpatch.observe( myobj );
myobj.firstName = "Albert";
myobj.contactDetails.phoneNumbers[0].number = "123";
var patches = jsonpatch.generate(observer);
// patches  == [
//   { op:"replace", path="/firstName", value:"Albert"},
//   { op:"replace", path="/contactDetails/phoneNumbers/0/number", value:"123"},
//   { op:"add", path="/contactDetails/phoneNumbers/1", value:{number:"456"}}];


In a web browser

  1. Testing json-patch.js
    • Load src/patchtest.html in your web browser
  2. Testing json-patch-duplex.js
    • Load src/test-duplex.html in your web browser

Each of the test suite files contains Jasmine unit test suite and JSLitmus performance test suite.

To run JSLitmus performance tests, press "Run Tests" button.

In Node.js

  1. Go to directory where you have cloned the repo
  2. Install Jasmine Node.js module by running command npm install jasmine-node -g
  3. Testing json-patch.js
    • Run command jasmine-node --matchall --config duplex no src/test.js
  4. Testing json-patch-duplex.js
    • Run command jasmine-node --matchall --config duplex yes src/test.js src/test-duplex.js


jsonpatch.apply (obj Object, patches Array) : boolean

Available in json-patch.js and json-patch-duplex.js

Applies patches array on obj.

If patch was succesfully applied, returns true. Otherwise returns false.

If there was a test patch in patches array, returns the result of the test.

If there was more then one patch in the array, the result of the last patch is returned.

jsonpatch.observe (obj Object, callback Function (optional)) : observer Object

Available in json-patch-duplex.js

Sets up an deep observer on obj that listens for changes in object tree. When changes are detected, the optional callback is called with the generated patches array as the parameter.

Returns observer.

jsonpatch.generate (obj Object, observer Object) : patches Array

Available in json-patch-duplex.js

If there are pending changes in obj, returns them synchronously. If a callback was defined in observe method, it will be triggered synchronously as well.

If there are no pending changes in obj, returns an empty array.

jsonpatch.unobserve (obj Object, observer Object) : void

Available in json-patch-duplex.js

Destroys the observer set up on obj.

Any remaining changes are delivered synchronously (as in jsonpatch.generate). Note: this is different that ES6/7 Object.unobserve, which delivers remaining changes asynchronously.


0.3.6 (Nov 14, 2013)


0.3.5 (Oct 28, 2013)


  • issues with calling observe/unobserve method on an object multiple times in Chrome (native Object.observe) (#20)

0.3.4 (Oct 16, 2013)


  • generate array item remove patches in reverse order, so they can be correctly applied in order they were generated (#16)

0.3.3 (Oct 11, 2013)


  • properly escape ~ and / characters in poiner paths (#19)
  • generated patch contained array length (only in native Object.observe version) (#14)
  • jsonpatch.unobserve now delivers pending changes immediately (previously last-minute changes could be lost)
  • stability fixes for browsers with native Object.observe (Chrome)
  • code cleanup
  • removed sourcemap reference from output js file
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