README.md

FlattenDeep

This module can be used to flatten a deeply nested array.

Example

Deeply nested array

import flattenDeep from 'flattenDeep'

flattenDeep([[1,2,[3]],[4,[5,[],[6,[7]]]],[8,[9,10]]]) //-> [1,2,3,4,5,6,7,8,9,10]

Empty array and other values

flattenDeep([]) //-> []

//empty nested array are discarded
flattenDeep([1,[[],2]]) //-> [1,2]

flattenDeep('a') //-> 'a'

flattenDeep(undefined) //-> undefined

flattenDeep.js

/** @module flattenDeep */

const isArray = Array.isArray

/**
 * Flatten a deeply nested array
 * @param {Array} nested - the array to flatten
 * @return {*|Array} The flattened array or the argument if it is not an array
 */
const flattenDeep = (nested) => {
  return !isArray(nested) ?
  nested : //base case, single element
    nested.reduce((acc, el) => { //flatten array
        return isArray(el) ?
            acc.concat(flattenDeep(el)) : //recurse
            acc.concat(el)        
    }, [] )
}

export default flattenDeep

flattenDeep.spec.js

import { expect } from 'chai'

suite('Flatten a deeply nested array', () => {
  
  test('deeply nested array', (done) => {
    const result = flattenDeep([[1,2,[3]],[4,[5,[],[6,[7]]]],[8,[9,10]]]) //-> [1,2,3,4,5,6,7,8,9,10]
    const expectedResult = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    expect(result).to.deep.equal(expectedResult)
    done()
  })
  
  test('empty array', (done) => {
    expect(flattenDeep([])).to.equal([])
    done()
  })
  
  test('empty nested array', (done) => {
    expect(flattenDeep([[[]]])).to.equal([])
    done()
  })
  
  test('empty nested array are discarded', (done) => {
    expect(flattenDeep([1,[[],2]]))).to.deep.equal([1,2])
  })
  
  test('undefined', (done) => {
    expect(flattenDeep(undefined)).to.equal(undefined))
  })
})