A leaner and meaner implementation of JSON-Patch. Small footprint. High performance.

With JSON-Patch, you can:

• apply patches
• validate a sequence of patches
• observe for changes (and generate patches when a change is detected)
• compare two objects (to obtain the difference)

JSON-Patch (RFC6902) is a 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.

1.22 KB minified and gzipped (3 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.
• ES7 Object.observe() is used when available.
• Tested in IE 8-11, Firefox, Chrome, Safari and Node.js

Install the current version (and save it as a dependency):

$ npm install fast-json-patch --save

$ bower install fast-json-patch --save

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

Call require to get the instance:

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

💡 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";
myobj.contactDetails.phoneNumbers.push({number:"456"});
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"}}];

Comparing two object trees:

var objA = {user: {firstName: "Albert", lastName: "Einstein"}};
var objB = {user: {firstName: "Albert", lastName: "Collins"}};
var diff = jsonpatch.compare(objA, objB));
//diff == [{op: "replace", path: "/user/lastName", value: "Collins"}]

Validating a sequence of patches:

var obj = {user: {firstName: "Albert"}};
var patches = [{op: "replace", path: "/user/firstName", value: "Albert"}, {op: "replace", path: "/user/lastName", value: "Einstein"}];
var errors = jsonpatch.validate(patches, obj);
if (errors.length == 0) {
 //there are no errors!
}
else {
  for (var i=0; i < errors.length; i++) {
    if (!errors[i]) {
      console.log("Valid patch at index", i, patches[i]);
    }
    else {
      console.error("Invalid patch at index", i, errors[i], patches[i]);
    }
  }
}

1. Testing json-patch.js

• Load test/SpecRunner.html in your web browser

2. Testing json-patch-duplex.js

• Load test/SpecRunnerDuplex.html in your web browser

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

To run Benchmark.js performance tests, press "Run Tests" button.

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 test/spec/coreSpec.js

4. Testing json-patch-duplex.js

• Run command jasmine-node --matchall --config duplex yes test/spec/coreSpec.js test/spec/duplexSpec.js

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

Applies patches array on obj.

If the validate parameter is set to true, the patch is extensively validated before applying. An invalid patch results in throwing an error (see jsonpatch.validate for more information about the error object).

If patch was succesfully applied, returns true.

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

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

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.

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 (length 0).

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.

Available in json-patch-duplex.js

Compares object trees obj1 and obj2 and returns the difference relative to obj1 as a patches array.

If there are no differences, returns an empty array (length 0).

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

Validates a sequence of operations. If tree parameter is provided, the sequence is additionally validated against the object tree.

If there are no errors, returns undefined. If there is an errors, returns a JsonPatchError object with the following properties:

• name String - short error code
• message String - long human readable error message
• index Number - index of the operation in the sequence
• operation Object - reference to the operation
• tree Object - reference to the tree

Possible errors:

As undefined is not a valid value for any JSON node, it's also not valid value o JSON Patch operation object value property. Therefore, for valid JSON document, jsonpatch will not generate JSON Patches that sets anything to undefined.

However, to play nicer with natural JavaScipt objects jsonpatch can be applied to an object that contains undefined, in such case we will treat it as JS does. .apply will handle JSON Patches with value: undefined as any other falsy value. .generate, .compare, .observe methods will also produce JSON Patches with undefineds, but only for (non valid) JSON documents that contains it.

As undefined is not a valid value for any JSON node, it's also not valid value o JSON Patch operation object value property. Therefore jsonpatch will not generate JSON Patches that sets anything to undefined.

However, to play nicer with natural JavaScipt objects jsonpatch can be applied to an object that contains undefined, in such case we will use it as native JSON.stringify - we will treat them as non-existing nodes, and map to null for array elements.

To see the list of recent changes, see Releases.