123456789101112131415161718
export function intersperse(separator, list){  if (arguments.length === 1) return _list => intersperse(separator, _list)
  let index = -1  const len = list.length  const willReturn = []
  while (++index < len){    if (index === len - 1){      willReturn.push(list[ index ])    } else {      willReturn.push(list[ index ], separator)    }  }
  return willReturn}