Bugs

current version will not dive into nested arrays; if there is tiniest bit different between nested arrays, the diff will emit replacement for the whole nested array as a single op.
there is no way of specifying if an array should be compared as unordered set of elements or ordered list of elements
the code is in dated coffeescript, needs rewrite in modern js, ideally with ts/flow annotations.

Summary

(R)emove-(U)pdate-(S)et JSON diff library can be used standalone to compute difference between two JSON objects.

Produced diff is MongoDB compatible and can be used to modify documents with collection.update(...).

Examples

Diff

a	b	diff(a, b)	options
`{a:1}`	`{b:2}`	`{$unset:{a:true},$set:{b:2}}`
`{a:1}`	`{b:1}`	`{$rename:{a:'b'}}`
`{a:1}`	`{}`	`{$unset:{a:true}}`
`{a:1}`	`{a:2.5}`	`{$set:{a:2.5}}`
`{a:1}`	`{a:2.5}`	`{$inc:{a:1.5}}`	`{inc:true}`

Apply

a	diff	apply(a, diff)
`{}`	`{$inc:{'a.b':1}}`	`{a:{b:1}}`
`{a:1.5}`	`{$inc:{a:-2.5}}`	`{a:-1}`
`{a:true}`	`{$rename:{a:'b'}}`	`{ b: true }`
`{a:1,b:2}`	`{$unset:{a:true},$set:{'c.d':3}}`	`{b:2,c:{d:3}}`

Usage

Install rus-diff in your project:

npm install rus-diff --save

Install ES6 compatibility layer:

npm install babel-polyfill --save

Usage example:

// Add ES6 polyfills.
require('babel-polyfill')

var diff = require('rus-diff').diff

var a = {
  foo: {
    bb: {
      inner: {
        this_is_a: 1,
        to_rename: "Hello"
      }
    },
    aa: 1
  },
  bar: 1,
  replace_me: 1
}

var b = {
  foo: {
    bb: {
      inner: {
        this_is_b: 2
      }
    },
    cc: {
      new_val: 2
    }
  },
  bar2: 2,
  zz: 2,
  renamed: "Hello",
  replace_me: 2
}

console.log(diff(a, b))

Produces diff:

{ '$rename': { 'foo.bb.inner.to_rename': 'renamed' },
  '$unset': { bar: true, 'foo.aa': true, 'foo.bb.inner.this_is_a': true },
  '$set':
   { bar2: 2,
     'foo.bb.inner.this_is_b': 2,
     'foo.cc': { new_val: 2 },
     replace_me: 2,
     zz: 2 } }

For more usage examples please see spec directory.

Exported functions:

// Generate diff between a and b JSON objects.
// prefix can be set to an array or string to scope (prefix) keys,
//   ie. 'foo.bar' means all changes will have keys starting with 'foo.bar...'.
// options.inc = true can be set to enable $inc part for number changes.
diff(a, b, prefix = [], options = {})

// Apply delta diff on the JSON object a. If you don't want to mutate a you
// can clone it before passing to apply:
//   apply(clone(a), delta)
apply(a, delta)

And some less important, utility functions:

// JSON object deep copy.
clone(a)

// Resolve key path on the object. Returns a tuple [a, path] where a
// is resolved object and path is an array of last component or multiple
// unresolved components.
//
// a - object
// path - an array or dot separated key path
//
// For example, having a document:
//
//   var a = { hello: { in: { nested: { world: '!' } } } }
//
//   resolve a, 'hello.in.nested'
//
// Returns [ { nested: { world: '!' } }, [ 'nested' ] ]
//
//   resolve a, 'hello.in.nested.something.other'
//
// Returns [ { world: '!' }, [ 'something', 'other' ] ]
//
resolve(a, path)

// Convert non array path into array based key path.
arrize(path)

License

The MIT License (MIT)

Copyright (c) 2014 Mirek Rusin

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.