Compactly represent an array of integers as a string using the base64 alphabet. 40% to 50% smaller output than JSON.stringify.

encodeIntArray.js

const TABLE = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'.split('')

function encodeInt (int) {
  let encoded = ''
  do {
    let offset = int & 0b011111
    int >>>= 5
    if (int === 0) {
      offset |= 0b100000
    }
    encoded += TABLE[offset]
  } while (int !== 0)
  return encoded
}

export function decodeIntArray (ser) {
  const arr = []
  const stringLength = ser.length
  let currentInt = 0
  let currentShift = 0

  for (let i = 0; i < stringLength; i++) {
    const char = ser.charAt(i)
    const offset = TABLE.indexOf(char)
    const numPart = offset & 0b011111
    const isEnd = !!(offset & 0b100000)

    currentInt |= (numPart << currentShift)
    currentShift += 5

    if (isEnd) {
      arr.push(currentInt)
      currentInt = 0
      currentShift = 0
    }
  }

  return arr
}

export function encodeIntArray (arr) {
  return arr.map(encodeInt).join('')
}