Underscore mixins for deeply nested objects

npm install underscore.deep
55 downloads in the last day
360 downloads in the last week
1 487 downloads in the last month


Underscore.deep is a collection of Underscore mixins that operate on nested objects.

This README is written in Literate CoffeeScript as a Mocha test suite, so you can execute all of the examples - just run:

make README.coffee.md


npm install underscore
npm install underscore.deep


_ = require 'underscore'
_.mixin require 'underscore.deep'


describe 'underscore.deep', ->
  assert = require 'assert'
  _ = require 'underscore'
  _.mixin require './underscore.deep'


Takes an object and produces a new object with no nested objects, converting any nested objects to sets of fields with dot-notation keys, recursively.

  describe '_.deepToFlat', ->

    it 'does nothing with shallow objects', ->
      assert.deepEqual _.deepToFlat({}),             {}
      assert.deepEqual _.deepToFlat( shallow: 1 ),   shallow: 1

    it 'deepToFlats nested objects', ->
      assert.deepEqual _.deepToFlat( deeply: { nested: 2 } ), 'deeply.nested': 2
      assert.deepEqual _.deepToFlat(
            first: 'Deep'
            last: 'Blue'
          age: 33
        'user1.name.first': 'Deep'
        'user1.name.last': 'Blue'
        'user1.age': '33'


Takes an object and produces a new object with no dot-notation keys, converting any set of dot-notation keys with the same prefix to a nested object, recursively.

Warning: Any keys with a dot (.) in the input object will be converted to nested objects, so if you use dots in your keys you may want to replace them before you call _.deepFromFlat.

  describe '_.deepFromFlat', ->
    it 'does nothing with objects with no dot-notation', ->
      assert.deepEqual _.deepFromFlat({}),             {}
      assert.deepEqual _.deepFromFlat( shallow: 1 ),   shallow: 1

    it 'deepFromFlats a flat object', ->
      assert.deepEqual _.deepFromFlat( 'deeply.nested': 2 ), deeply: { nested: 2 }
      assert.deepEqual _.deepFromFlat(
        'user1.name.first': 'Deep'
        'user1.name.last': 'Blue'
        'user1.age': '33'
            first: 'Deep'
            last: 'Blue'
          age: 33

.deepToFlat and .deepFromFlat

Taken as a pair, _.deepToFlat and _.deepFromFlat have an interesting relationship:

  describe '_.deepToFlat and _.deepFromFlat', ->
    it 'they undo each other', ->
      deepObj = a: 1, b: { c: 2 }
      flatObj = a: 1, 'b.c': 2
      assert.deepEqual flatObj, _.deepToFlat deepObj
      assert.deepEqual deepObj, _.deepFromFlat flatObj

They are inverses (of a sort)! We can reformulate this as a property that holds for any flatObj and deepObj:

      assert.deepEqual flatObj, _.deepToFlat _.deepFromFlat flatObj
      assert.deepEqual deepObj, _.deepFromFlat _.deepToFlat deepObj


Takes an object and makes a copy of it, recursively copying any nested objects or arrays. Instances of classes, like Number or String, are not cloned.

  describe '_.deepClone', ->

    orig =
          quote: 'Computer science is no more about computers' +
            'than astronomy is about telescopes.'
          sayer: 'Dijkstra'
        pools: [
          { depth: 10 }
          { depth: 20 }
          { depth: 30 }

    it 'clones an object deeply', ->
      copy = _.deepClone orig
      assert.deepEqual copy, orig
      assert.notStrictEqual copy, orig
      assert.notStrictEqual copy.deepThings.proverbs, orig.deepThings.proverbs
      assert.notStrictEqual copy.deepThings.pools, orig.deepThings.pools

    it 'is equivalent to the composition of _.deepFromFlat, _.clone, and _.deepToFlat', ->
      copy2 = _.deepFromFlat _.clone _.deepToFlat orig
      assert.deepEqual copy2, orig
      assert.notEqual copy2, orig

_.deepHas(obj, key)

Takes an object obj and a string key (which should be a dot-notation key) and returns true if obj has a nested field named key.

  describe '_.deepHas', ->

    obj = we: have: to: go: 'deeper'

    it 'returns true if a regular key exists', ->
      assert.equal _.deepHas(obj, 'we'), true

    it 'returns true if the deep key exists', ->
      assert.equal _.deepHas(obj, 'we.have'), true
      assert.equal _.deepHas(obj, 'we.have.to'), true
      assert.equal _.deepHas(obj, 'we.have.to.go'), true

    it 'returns false if the deep key does not exist', ->
      assert.equal _.deepHas(obj, 'we.have.to.goop'), false

    it 'is not equivalent to the composition of _.has and _.deepToFlat', ->
      assert.equal _.deepHas(obj, 'we.have.to.go'), _.has(_.deepToFlat(obj), 'we.have.to.go')
      assert.equal _.deepHas(obj, 'we.have.to.goop'), _.has(_.deepToFlat(obj), 'we.have.to.goop')
      assert.notEqual _.deepHas(obj, 'we'), _.has(_.deepToFlat(obj), 'we')


Takes an object and returns all of its nested keys in dot-notation.

If you think of a deeply-nested object as a tree, then it will return the paths to all of the tree's leaves. That means it won't return intermediate keys. As a consequence, _.deepHas(obj, key) is not equivalent to _.contains _.deepKeys(obj), key.

  describe '_.deepKeys', ->

    obj =
        leaf1: 1
          leaf2: 2
          leaf3: 3

    it 'returns dot-notation keys for only the leaf fields of an object', ->
      assert.deepEqual _.deepKeys(obj), [

    it 'is equivalent to the composition of _.keys and _.deepToFlat', ->
      assert.deepEqual _.deepKeys(obj), _.keys(_.deepToFlat obj)

    it 'does not make _.deepHas equivalent to the composition of _.contains and _.deepKeys', ->
      assert.notDeepEqual _.contains(_.deepKeys(obj), 'node1'), _.has(obj, 'node1')

_.deepExtend(destination, source, mutate = false)

Takes an object destination and an object source and creates a new object with all the deep fields of destination and all the deep fields of source. Any deep fields with the same deep key in destination and source will have the value from source (so source fields overwrite destination fields).

Unlike _.extend, _.deepExtend is pure, so the original objects destination and source will not be modified. If you really want to mutate destination by adding the deep fields of source, pass true as the third parameter mutate.

  describe '_.deepExtend', ->

    destination =
      name: 'heaven'
        michael: true

    it 'combines all the deep fields of destination and source', ->
      assert.deepEqual _.deepExtend(destination, { angels: gabriel: false }),
        name: 'heaven'
          michael: true
          gabriel: false

    it 'overwrites fields of destination with fields from source', ->
      assert.deepEqual _.deepExtend(destination, { angels: michael: false }),
        name: 'heaven'
          michael: false

    it 'does not mutate the input objects', ->
      assert.notStrictEqual destination, _.deepExtend(destination, { name: 'hell' })

    it 'is equivalent to a weird composition of _.deepFromFlat, _.extend, and _.deepToFlat', ->
      assert.deepEqual _.deepExtend(destination, { angels: gabriel: false }),
        _.deepFromFlat _.extend _.deepToFlat(destination), _.deepToFlat({ angels: gabriel: false })

_.deepMapValues(obj, func)

Like _.mapValues, but for deep objects. Constructs a new object by applying function func to the value for every deep field in object obj.

  describe '_.deepMapValues', ->
    obj =
        empathy: true
        responsibility: false

    it 'creates an object by applying func to each deep value in obj', ->
      assert.deepEqual _.deepMapValues(obj, (v) -> not v),
          empathy: false
          responsibility: true

    it 'is equivalent to the composition of _.deepFromFlat, _.mapValues, and _.deepToFlat', ->
      assert.deepEqual _.deepMapValues(obj, (v) -> String v),
        _.deepFromFlat _.mapValues _.deepToFlat(obj), (v) -> String v

Non-deep Helpers

Someday these will probably be moved into their own library, but for now they live here.


Takes a value val and returns true if it's a vanilla JS object (i.e. not an instance of any built-in or custom class). Otherwise returns false.

  describe '_.isPlainObject', ->

    it 'returns true for vanilla objects', ->
      assert.equal _.isPlainObject({}), true
      assert.equal _.isPlainObject({ vanilla: 'is so plain' }), true

    it 'returns false for other values', ->
      assert.equal _.isPlainObject(1), false
      assert.equal _.isPlainObject('chocolate'), false
      assert.equal _.isPlainObject(new Date()), false

_.mapValues(obj, func)

Takes an object obj and a function func and constructs a new object by applying func to every value in obj. func receives two arguments, the value and the key for that value.

Some have described this function as "the fundamental map over dictionaries." Others have said its not "mainstream enough to deserve to make it into Underscore proper." We take no stance in the debate, but we have to admit we use it on the daily.

  describe '_.mapValues', ->
    obj =
      respect: 1
      fairness: 2

    it 'creates an object by applying func to each value in obj', ->
      assert.deepEqual _.mapValues(obj, (v) -> v * 10),
        respect: 10
        fairness: 20

_.mapKeys(obj, func)

Exactly like _.mapValues but for keys.

Note that the function takes a function takes a key and optionally a value, not the usual mapping function pattern of taking a value and optionally a key

  describe '_.mapKeys', ->
    obj =
      animate: 1
      charge: 2

    it 'creates an object by applying func to each key in obj', ->
      assert.deepEqual _.mapKeys(obj, (key) -> 're' + key),
        reanimate: 1
        recharge: 2

    it 'creates an object by applying func to each key, val in obj', ->
      assert.deepEqual _.mapKeys(obj, (key, val) -> 're' + key + val),
        reanimate1: 1
        recharge2: 2
npm loves you