deepmerge

What is deepmerge?

The deepmerge npm package is a library for deep (recursive) merging of Javascript objects. It is useful for combining objects with nested structures, such as configuration settings or state objects in applications.

What are deepmerge's main functionalities?

Merging two objects

This feature allows you to merge two objects deeply. Properties from the second object will be added to the first, and if properties are objects themselves, they will be merged recursively.

{"const merge = require('deepmerge');
const x = { foo: { bar: 3 } };
const y = { foo: { baz: 4 } };
const z = merge(x, y);
console.log(z); // { foo: { bar: 3, baz: 4 } }"}

Merging with array concatenation

This feature allows you to specify how arrays are merged. By default, arrays are merged by concatenation, but you can provide a custom arrayMerge function.

{"const merge = require('deepmerge');
const x = { foo: [1, 2, 3] };
const y = { foo: [4, 5, 6] };
const z = merge(x, y, { arrayMerge: (destinationArray, sourceArray) => destinationArray.concat(sourceArray) });
console.log(z); // { foo: [1, 2, 3, 4, 5, 6] }"}

Merging with array replacement

This feature allows you to replace the destination array with the source array instead of merging or concatenating them.

{"const merge = require('deepmerge');
const x = { foo: [1, 2, 3] };
const y = { foo: [4, 5, 6] };
const z = merge(x, y, { arrayMerge: (destinationArray, sourceArray) => sourceArray });
console.log(z); // { foo: [4, 5, 6] }"}

Merging with custom options

This feature allows you to provide custom merge functions to handle the merging process according to your specific requirements.

{"const merge = require('deepmerge');
const x = { foo: { bar: 3 } };
const y = { foo: { bar: 4, baz: 5 } };
const overwriteMerge = (destinationArray, sourceArray, options) => sourceArray;
const z = merge(x, y, { arrayMerge: overwriteMerge });
console.log(z); // { foo: { bar: 4, baz: 5 } }"}

Other packages similar to deepmerge

lodash.merge

Lodash provides a merge function that can recursively merge own and inherited enumerable string keyed properties of source objects into the destination object. It's similar to deepmerge but is part of the larger lodash utility library.

extend

The extend package is a port of the jQuery.extend method that can deep copy both arrays and objects. It is less specialized than deepmerge and does not provide as many options for customizing the merge behavior.

object-assign-deep

This package offers functionality similar to Object.assign but with deep merging capabilities. It is a smaller and more focused utility compared to deepmerge, but it may not offer the same level of customization for array merging and other specific use cases.

README

deepmerge

Merge the enumerable attributes of two objects deeply.

example

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

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' } ] }

console.log(util.inspect(merge(x, y), false, null))

output:

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

methods

var merge = require('deepmerge')

merge(x, y)

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.

The merge is immutable, so neither x nor y will be modified.

The merge will also merge arrays and array values.

install

With npm do:

npm install deepmerge

test

With npm do:

npm test