Promise.finally

const Gen = (time) => {
  return new Promise((resolve, reject) => {
    setTimeout(function () {
      if(time < 500) {
        reject(time)
      } else {
        resolve(time)
      }
    },time)
  })
}

Gen(Math.random() * 1000)
.then(val => console.log('resolve', val))
.catch(err => console.log('reject', err))
.finally(() => { console.log('finish')})