Flatten an array of nested arrays

flattenArray.js

/*
 * This function returns a flat array given an array of arbitrarily nested arrays 
 * e.g. [[1,2,[3]],4] -> [1,2,3,4]. 
 */
const flattenArray = arr => {
  const result = []
  arr.map(item => {
    if (Array.isArray(item)) {
      result.push(...flattenArray(item))
    } else {
      result.push(item)
    }
  })
  return result
}