// merge 1-2 arrays
export default function concat2(
  set1?: any[] | string | undefined,
  set2?: any[] | string | undefined
) {
  let idx
  const len1 = set1.length
  const len2 = set2.length
  const result = []

  if (process.env.NODE_ENV !== 'production') {
    if (Array.isArray(set1) === false) {
      console.warn('provided non array to concat(HERE, []): ', set1)
    }
    if (Array.isArray(set2) === false) {
      console.warn('provided non array to concat([], HERE): ', set2)
    }
  }

  idx = 0
  while (idx < len1) {
    result[result.length] = set1[idx]
    idx += 1
  }

  idx = 0
  while (idx < len2) {
    result[result.length] = set2[idx]
    idx += 1
  }
  return result
}