Flatten a n-dimensional nested Javascript array

flattenDeep.js

/*
 * Flatten deeply nested array without external library like Immutable
 * Simplified ES6 version of lodash flattenDeep functionality
 * Reference: https://lodash.com/docs#flattenDeep
 * Requirements: Latest Chrome/FF browser or ES6 transpiler like Babel
*/
const INFINITY = 1 / 0

/*
 * Utility flatten array function
 * @param array: array
 * @param depth : number
 * @param isStrict : boolean
*/
const baseFlatten = (array, depth, result) => {
  let index = -1
  let length = array.length
  result || (result = [])

  while (++index < length) {
    let value = array[index]
    if (depth > 0 && Array.isArray(value)) {
      if (depth > 1) {
        // Recursively flatten arrays (susceptible to call stack limits).
        baseFlatten(value, depth - 1, result)
      } else {
        result.push(value)
      }
    } else {
      result.push(value)
    }
  }
  return result;
}

/*
 * Flatten a deep array function
 * @param array : array
*/
const flattenDeep = (array) => {
  const length = array ? array.length : 0
  return length ? baseFlatten(array, INFINITY) : []
}

// test
const arr = [[1,2,[3]],4]
console.log(flattenDeep(arr))