@sumor/short-id/src/decode.js

This is a short-id library for Node.js and the browser. You can easily use it to generate a short id from number.

export default (code, rule) => {
  const chars = rule
  const radix = chars.length
  code = String(code)
  const len = code.length
  let i = 0
  let number = 0
  while (i < len) {
    number += radix ** i++ * chars.indexOf(code.charAt(len - i) || 0)
  }
  return number
}