deepmerge

Merges the enumerable attributes of two or more objects deeply.

UMD bundle is 587B minified+gzipped

Migration from 1.x to 2+

Check out the changes from version 1.x to 2.0.0

For the legacy array element-merging algorithm, see the arrayMerge option below.

Getting Started

Example Usage

const x = {
	foo: { bar: 3 },
	array: [{
		does: 'work',
		too: [ 1, 2, 3 ]
	}]
}

const y = {
	foo: { baz: 4 },
	quux: 5,
	array: [{
		does: 'work',
		too: [ 4, 5, 6 ]
	}, {
		really: 'yes'
	}]
}

const expected = {
	foo: {
		bar: 3,
		baz: 4
	},
	array: [{
		does: 'work',
		too: [ 1, 2, 3 ]
	}, {
		does: 'work',
		too: [ 4, 5, 6 ]
	}, {
		really: 'yes'
	}],
	quux: 5
}

merge(x, y) // => expected

Installation

With npm do:

npm install deepmerge

deepmerge can be used directly in the browser without the use of package managers/bundlers as well: UMD version from unpkg.com.

Include

deepmerge exposes a CommonJS entry point:

const merge = require('deepmerge')

The ESM entry point was dropped due to a Webpack bug.

API

`merge(x, y, [options])`

Merge two objects x and y deeply, returning a new merged object with the elements from both x and y.

If an element at the same key is present for both x and y, the value from y will appear in the result.

Merging creates a new object, so that neither x or y is modified.

Note: By default, arrays are merged by concatenating them.

`merge.all(arrayOfObjects, [options])`

Merges any number of objects into a single result object.

const x = { foo: { bar: 3 } }
const y = { foo: { baz: 4 } }
const z = { bar: 'yay!' }

const expected = { foo: { bar: 3, baz: 4 }, bar: 'yay!' }

merge.all([x, y, z]) // => expected

Options

`arrayMerge`

There are multiple ways to merge two arrays, below are a few examples but you can also create your own custom function.

Overwrite Array

Overwrites the existing array values completely rather than concatenating them

const overwriteMerge = (destinationArray, sourceArray, options) => sourceArray

merge(
	[1, 2, 3],
	[3, 2, 1],
	{ arrayMerge: overwriteMerge }
) // => [3, 2, 1]

Combine Array

Combine arrays, such as overwriting existing defaults while also adding/keeping values that are different names

To use the legacy (pre-version-2.0.0) array merging algorithm, use the following:

const emptyTarget = value => Array.isArray(value) ? [] : {}
const clone = (value, options) => merge(emptyTarget(value), value, options)

const combineMerge = (target, source, options) => {
	const destination = target.slice()

	source.forEach((item, index) => {
		if (typeof destination[index] === 'undefined') {
			const cloneRequested = options.clone !== false
			const shouldClone = cloneRequested && options.isMergeableObject(item)
			destination[index] = shouldClone ? clone(item, options) : item
		} else if (options.isMergeableObject(item)) {
			destination[index] = merge(target[index], item, options)
		} else if (target.indexOf(item) === -1) {
			destination.push(item)
		}
	})
	return destination
}

merge(
	[{ a: true }],
	[{ b: true }, 'ah yup'],
	{ arrayMerge: combineMerge }
) // => [{ a: true, b: true }, 'ah yup']

`isMergeableObject`

By default, deepmerge clones every property from almost every kind of object.

You may not want this, if your objects are of special types, and you want to copy the whole object instead of just copying its properties.

You can accomplish this by passing in a function for the isMergeableObject option.

If you only want to clone properties of plain objects, and ignore all "special" kinds of instantiated objects, you probably want to drop in is-plain-object.

const isPlainObject = require('is-plain-object')

function SuperSpecial() {
	this.special = 'oh yeah man totally'
}

const instantiatedSpecialObject = new SuperSpecial()

const target = {
	someProperty: {
		cool: 'oh for sure'
	}
}

const source = {
	someProperty: instantiatedSpecialObject
}

const defaultOutput = merge(target, source)

defaultOutput.someProperty.cool // => 'oh for sure'
defaultOutput.someProperty.special // => 'oh yeah man totally'
defaultOutput.someProperty instanceof SuperSpecial // => false

const customMergeOutput = merge(target, source, {
	isMergeableObject: isPlainObject
})

customMergeOutput.someProperty.cool // => undefined
customMergeOutput.someProperty.special // => 'oh yeah man totally'
customMergeOutput.someProperty instanceof SuperSpecial // => true

`customMerge`

Specifies a function which can be used to override the default merge behavior for a property, based on the property name.

The customMerge function will be passed the key for each property, and should return the function which should be used to merge the values for that property.

It may also return undefined, in which case the default merge behaviour will be used.

const alex = {
    name: {
        first: 'Alex',
        last: 'Alexson'
    },
    pets: ['Cat', 'Parrot']
}

const tony = {
    name: {
        first: 'Tony',
        last: 'Tonison'
    },
    pets: ['Dog']
}

const mergeNames = (nameA, nameB) => `${nameA.first} and ${nameB.first}`

const options = {
    customMerge: (key) => {
        if (key === 'name') {
            return mergeNames
        }
    }
}

const result = merge(alex, tony, options)

result.name // => 'Alex and Tony'
result.pets // => ['Cat', 'Parrot', 'Dog']

`clone`

Deprecated.

Defaults to true.

If clone is false then child objects will be copied directly instead of being cloned. This was the default behavior before version 2.x.

Testing