Creating anonymous UUID in JavaScript using combination of IP address and User-Agent

getUUID.js

const getUUID = (
    service='https://api.ipify.org/?format=json',
    key='ip'
) => { 
    return new Promise(
        (resolve, reject) => {
          fetch(service)
          .then((r) => r.json())
          .then((j) => {
              let r = /\D+/g
              let h = String(
                  window.navigator.userAgent.replace(r, ''
                  ) * j[key].replace(r, '')
              ).replace(r, '').replace('0', '').split('')
              let g = () => Math.floor(h.shift() * 0x10000)
              resolve(g() + g() + '-' + g() + '-' + g() + '-' + 
                      g() + '-' + g() + g() + g())
          }).catch((e) => reject('failed to create UUID'))
        }
    )
}

// Excute it
getUUID().then((d) => console.log(d)).catch((e) => console.warn(e))