deep-diff is a javascript/node.js module providing utility functions for working with the structural differences between objects.

• Get the structural differences between two objects.
• Observe the structural differences between two objects.
• When structural differences represent change, apply change from one object to another.
• When structural differences represent change, selectively apply change from one object to another.

npm install deep-diff

For the browser, you can install with bower:

bower install deep-diff

Tests use mocha and expect.js, so if you clone the github repository you'll need to run:

npm install

... followed by ...

npm test

... or ...

mocha -R spec

nodejs

var deep = require('deep-diff')

browser

<script src="deep-diff-0.1.3.min.js"></script>

Minified, browser release of the current version of the module is under the releases folder. In a browser, deep-diff defines a global variable DeepDiff. If there is a conflict in the global namesapce you can restore the conflicting definition and assign deep-diff to another variable like this: var deep = DeepDiff.noConflict();.

In order to describe differences, change revolves around an origin object. For consistency, the origin object is always the operand on the left-hand-side of operations. The comparand, which may contain changes, is always on the right-hand-side of operations.

var diff = require('deep-diff').diff;

var lhs = {
	name: 'my object',
	description: 'it\'s an object!',
	details: {
		it: 'has',
		an: 'array',
		with: ['a', 'few', 'elements']
	}
};

var rhs = {
	name: 'updated object',
	description: 'it\'s an object!',
	details: {
		it: 'has',
		an: 'array',
		with: ['a', 'few', 'more', 'elements', { than: 'before' }]
	}
};

var differences = diff(lhs, rhs);

The code snippet above would result in the following structure describing the differences:

[ { kind: 'E',
    path: [ 'name' ],
    lhs: 'my object',
    rhs: 'updated object' },
  { kind: 'A',
    path: [ 'details', 'with' ],
    index: 2,
    item: { kind: 'E', path: [], lhs: 'elements', rhs: 'more' } },
  { kind: 'A',
    path: [ 'details', 'with' ],
    index: 3,
    item: { kind: 'N', rhs: 'elements' } },
  { kind: 'A',
    path: [ 'details', 'with' ],
    index: 4,
    item: { kind: 'N', rhs: { than: 'before' } } } ]

Differences are reported as one or more change records. Change records have the following structure:

• kind - indicates the kind of change; will be one of the following:
  • N - indicates a newly added property/element
  • D - indicates a property/element was deleted
  • E - indicates a property/element was edited
  • A - indicates a change occurred within an array
• path - the property path (from the left-hand-side root)
• lhs - the value on the left-hand-side of the comparison (undefined if kind === 'N')
• rhs - the value on the right-hand-side of the comparison (undefined if kind === 'D')
• index - when kind === 'A', indicates the array index where the change occurred
• item - when kind === 'A', contains a nested change record indicating the change that occurred at the array index

Change records are generated for all structural differences between origin and comparand. The methods only consider an object's own properties and array elements; those inherited from an object's prototype chain are not considered.

Changes to arrays are recorded simplistically. We care most about the shape of the structure; therefore we don't take the time to determine if an object moved from one slot in the array to another. Instead, we only record the structural differences. If the structural differences are applied from the comparand to the origin then the two objects will compare as "deep equal" using most isEqual implementations such as found in lodash or underscore.

When two objects differ, you can observe the differences as they are calculated and selectively apply those changes to the origin object (left-hand-side).

var observableDiff = require('deep-diff').observableDiff,
applyChange        = require('deep-diff').applyChange;

var lhs = {
	name: 'my object',
	description: 'it\'s an object!',
	details: {
		it: 'has',
		an: 'array',
		with: ['a', 'few', 'elements']
	}
};

var rhs = {
	name: 'updated object',
	description: 'it\'s an object!',
	details: {
		it: 'has',
		an: 'array',
		with: ['a', 'few', 'more', 'elements', { than: 'before' }]
	}
};

observableDiff(lhs, rhs, function (d) {
	// Apply all changes except those to the 'name' property...
	if (d.path.length !== 1 || d.path.join('.') !== 'name') {
		applyChange(lhs, rhs, d);
	}
});

A standard import of var diff = require('deep-diff') is assumed in all of the code examples. The import results in an object having the following public properties:

• diff - a function that calculates the differences between two objects.
• observableDiff - a function that calculates the differences between two objects and reports each to an observer function.
• applyDiff - a function that applies any structural differences from one object to another.
• applyChange - a function that applies a single change record to an origin object.