A function that reduces a list of multiple nested list to a single list containing all its values

flatten.js

/*
  recursive calls to flatten will append items of inner array to the accumulator
  e.g flatten :: [[1,2,[3]],4] -> [1,2,3,4]
*/
	
const flatten = list => {
  if (!Array.isArray(list))  
    throw new Error(`Expecting input of type Array but found ${typeof list}`)
  return list.reduce((accumulator, item) =>
     accumulator.concat(Array.isArray(item) ? flatten(item) : item),
  [])	
}