From or to decimal notation

index.ts

const ALPHABET = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
const MIN_RADIX = 2
const MAX_RADIX = ALPHABET.length

function chekRadix(radix: number): void {
  if (radix < MIN_RADIX || radix > MAX_RADIX) {
    throw new Error(`radix argument must be between ${MIN_RADIX} and ${MAX_RADIX}`)
  }
}

function toDecimalNumber(value: string, radix = MAX_RADIX): number {
  chekRadix(radix)

  let result = 0

  let valueLength = value.length
  const lastIndex = valueLength - 1

  for (let index = 0; index < valueLength; index += 1) {
    result = result + ALPHABET.indexOf(value[lastIndex - index]) * radix ** index
  }

  return result
}

function fromDecimanNumber(value: number, radix = MAX_RADIX): string {
  chekRadix(radix)

  if (value === 0) {
    return '0'
  }

  let result = ''

  let localValue = value
  let prefix = ''

  if (value < 0) {
    localValue *= -1
    prefix = '-'
  }

  while (localValue > 0) {
    result = ALPHABET[localValue % radix] + result

    localValue = Math.floor(localValue / radix)
  }

  return prefix + result
}

console.log('****')
console.log(fromDecimanNumber(1000000000000, 2) === (1000000000000).toString(2))
console.log(toDecimalNumber('1000000000000', 36) === parseInt('1000000000000', 36))