Poll backend endpoint in Vanilla js

#javascript #polling

Senario

You need to poll for status of an task until completed. Once it is completed you need to run some js code.

Code

// lib/poll.js
export const timeout = n => new Promise(resolve => setTimeout(resolve, n))

/*
  @fn: (any) => any Function to be executed
  @condition: (res) => Boolean Function to test if we can stop polling
  @maxTries: number Max number of calls allowed before rejection of promise
  @gap: number Minimum time (in ms) between two polls
*/
export const poll = async (fn, condition, maxTries, gap) => {
  while(maxTries--) {
    await timeout(gap)
    const result = await fn()
    if (condition(result)) return result
  }

  throw new Error('Poll Timeout')
}

Usage

const fetchStatus = () => this.$axios.get(`/orders/23222/status`)

poll(fetchStatus, ({status}) => status != 'PENDING', 30, 1000)
  .then(result => console.log(result)) // success!!
  .catch(err => { ... }) // either Timeout or XHR failed with error