deepmerge
=========

> UMD bundle is 567B minified+gzipped

Merge the enumerable attributes of two objects deeply.

[***Check out the changes from version 1.x to 2.0.0***](https://github.com/KyleAMathews/deepmerge/blob/master/changelog.md#200)

For the old array element-merging algorithm, see [the `arrayMerge` option below](#arraymerge).

## Webpack bug

If you have `require('deepmerge')` (as opposed to `import merge from 'deepmerge'`) anywhere in your codebase, Webpack 3 and 4 have a bug that [breaks bundling](https://github.com/webpack/webpack/issues/6584).

If you see `Error: merge is not a function`, add this alias to your Webpack config:

```
alias: {
	deepmerge$: path.resolve(__dirname, 'node_modules/deepmerge/dist/umd.js'),
}
```

example
=======

<!--js
var merge = require('./')
-->

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

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

var 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
```

methods
=======

```
var merge = require('deepmerge')
```

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` are be modified.

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

Merges any number of objects into a single result object.

```js
var x = { foo: { bar: 3 } }
var y = { foo: { baz: 4 } }
var z = { bar: 'yay!' }

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

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

### options

#### arrayMerge

The merge will also concatenate arrays and merge array values by default.

However, there are nigh-infinite valid ways to merge arrays, and you may want to supply your own.  You can do this by passing an `arrayMerge` function as an option.

The options object will include the default `isMergeableObject` implementation if the top-level consumer didn't pass a custom function in.

```js
function overwriteMerge(destinationArray, sourceArray, options) {
	return sourceArray
}
merge(
	[1, 2, 3],
	[3, 2, 1],
	{ arrayMerge: overwriteMerge }
) // => [3, 2, 1]
```

To prevent arrays from being merged:

```js
const dontMerge = (destination, source) => source
const output = merge({ coolThing: [1,2,3] }, { coolThing: ['a', 'b', 'c'] }, { arrayMerge: dontMerge })
output // => { coolThing: ['a', 'b', 'c'] }
```

To use the old (pre-version-2.0.0) array merging algorithm, pass in this function:

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

function oldArrayMerge(target, source, options) {
	const destination = target.slice()

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

merge(
	[{ a: true }],
	[{ b: true }, 'ah yup'],
	{ arrayMerge: oldArrayMerge }
) // => [{ 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`](https://github.com/jonschlinkert/is-plain-object).

```js
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
```

#### 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.

install
=======

With [npm](http://npmjs.org) do:

```sh
npm install deepmerge
```

Just want to download the file without using any package managers/bundlers?  [Download the UMD version from unpkg.com](https://unpkg.com/deepmerge/dist/umd.js).

test
====

With [npm](http://npmjs.org) do:

```sh
npm test
```

license
=======

MIT