12345678910111213141516
import {_isArray} from './_internals/_isArray'
export function flatten(list, input) {  const willReturn = input === undefined ? [] : input
  for (let i = 0; i < list.length; i++) {    if (_isArray(list[i])) {      flatten(list[i], willReturn)    } else {      willReturn.push(list[i])    }  }
  return willReturn}