cancel the ajax call after settled time.

cancelPromise.js

const fakeAjax = (time, cb) => {
  setTimeout(() => {cb('data...')}, time)
}

const noopPromise = new Promise(() => {})

// cancel promise when timeout reached, using Promise.race
const timer = (fn, time) =>
  Promise
    .race([
      new Promise(fn),
      new Promise((resolve, reject) => {
        setTimeout(() => {reject(Error('time out'))}, time)
      })
    ])
    .catch(
      // stop the chain, coz it is pending.
      () => noopPromise
    )


timer(
  function (resolve, reject) {
    // data fetched after 2s
    fakeAjax(500, resolve)
  },
  // cancel after 2s
  1000
)
  // not called.
  .then(data => {console.log(data)})