JavaScript simple string encoder/decoder written in TypeScript

string-codec.ts

// see [Inspiration Source](https://www.geeksforgeeks.org/decode-the-string-encoded-with-the-given-algorithm/)

// JavaScriptSimpleEncoder => iSmtpplierEcnScaovdaeJr
const encodeString = (inputStr: string): string => {
  const len = inputStr.length

  if (!len) return inputStr

  const isLenEven = len % 2 === 0

  const str: string = isLenEven ? `${inputStr} ` : inputStr
  const halfLength: number = Math.floor(len / 2)
  let result: string = str[halfLength]

  for (let i = 1; i <= halfLength; i += 1) {
    result += str[halfLength - i]
    result += str[halfLength + i]
  }

  if (isLenEven) return result.slice(0, len)

  return result
}

                                 
// iSmtpplierEcnScaovdaeJr => JavaScriptSimpleEncoder
const decodeString = (str: string): string => {
  const len = str.length

  if (!len) return str

  let result = str[0]
  let factor = -1

  for (let i = 1; i < len; i += 1) {
    result = factor > 0 ? result + str[i] : str[i] + result
    factor *= -1
  }

  return result
}