Flatten an array of arbitrarily nested arrays of integers into a flat array of integers. e.g. [[1,2,[3]],4] -> [1,2,3,4]

README.md

flatten

Flatten an array of arbitrarily nested arrays of integers into a flat array of integers.

Usage

// Both CommonJS and ES6 import syntaxes are supported
// import flatten from './flatten'
const flatten = require('./flatten')

flatten([[1,2,[3]],4]) // [1, 2, 3 , 4]

Test

Launch

node flatten.test.js

License

MIT

flatten.js

/**
 * flatten
 * @function
 *
 * Flatten an array of arbitrarily nested arrays of integers into a flat array of integers. e.g. [[1,2,[3]],4] -> [1,2,3,4]
 *
 * example usage:
 *
 * flatten([[1,2,[3]],4]) // [1, 2, 3 , 4]
 *
 * @param {Array} input
 * @returns {Array} output
 *
 * License: MIT
 * Author: Rob Jones
 */

function flatten (input) {
  // If the input is an array, flatten it with a recursive reducer.
  if (Array.isArray(input)) {
    return input.reduce(
      function flattener (result, value) {
        if (Array.isArray(value)) {
          // If value is an array, flatten it recursively
          return result.concat(value.reduce(flattener, []))
        } else {
          // If it's not an array append it to the result
          return result.concat(value)
        }
      }
      , []
    )
  } else {
    throw new TypeError('Argument must be an array')
  }
}

// CommonJS / ES6 export
module.exports = exports.default = flatten

flatten.test.js

// To run this test, launch
//
// node flatten.test.js
const assert = require('assert')

const flatten = require('./flatten')

const tests = [
  {
    input: [[1,2,[3]],4],
    output: [1, 2, 3, 4]
  },
  {
    input: [],
    output: []
  },
  {
    input: [1, [2, [3, [4, 5, [6, 7]], 8]]],
    output: [1, 2, 3, 4, 5, 6, 7, 8,]
  }
]


tests.forEach(({ input, output }) => {
  assert.deepEqual(flatten(input), output)
})

console.log(`run ${tests.length} tests`)