retry-task

Retry a Task a given number of times until it succeeds.

The module is built for use with Folktale's Task monad (data.task).

Usage

The module exports an object with two functions.

retry(retries, fn)

The function accepts a number of retries indicating the maximum number of retries and fn, a function that returns a task. Note that the number of retries excludes the initial trial before failure. I.e. if fn always fails and retries = 2 then fn will be called three times in total.

delayedRetry(retries, delay, fn)

The function accepts a number of retries indicating the maximum number of retries (see above). The delay parameter can be either a number, indicating the time to wait between retries in milliseconds, or a function that returns such a number. A delay function is called before each retry with the next attempt number (1, 2, 3, ...) as the first parameter. The fn parameter is a function that returns a task.

Miscellaneous

Both functions are curried.

Examples

retry

const fetch = require('isomorphic-fetch')
const Task = require('data.task')
const { retry } = require('retry-task')

const fork = t =>
  t.fork(console.error, console.log)

// Basic
let calls = 0
const failTwice = () =>
  new Task((rej, res) =>
    calls++ >= 2 ? res('All good!') : rej('nope'))

const basic1 = retry(2, failTwice)
fork(basic1)

const alwaysFail = () =>
  new Task(rej => rej('ALWAYS BLUE!'))
const basic2 = retry(2, alwaysFail)

fork(basic2)

// Fetching URLs with retries
const fetchUrl = url =>
  new Task((rej, res) =>
    fetch(url)
      .then(r => res(`[${r.status}] ${r.statusText}`))
      .catch(rej))

const npm = retry(3, () => fetchUrl('http://www.npmjs.com/'))
fork(npm)

// since the function is curried we can also do this
const withRetries = retry(3)
const npm2 = withRetries(() => fetchUrl('http://www.npmjs.com/'))
const google = withRetries(() => fetchUrl('http://www.google.com/'))
fork(npm2)
fork(google)

delayedRetry

const fetch = require('isomorphic-fetch')
const Task = require('data.task')
const { delayedRetry } = require('retry-task')

const fork = t =>
  t.fork(console.error, console.log)

// Basic
let calls = 0
const failTwice = () =>
  new Task((rej, res) =>
    calls++ >= 2 ? res('All good!') : rej('nope'))

const basic1 = delayedRetry(2, 1000, failTwice)
fork(basic1)

const alwaysFail = () =>
  new Task(rej => rej('ALWAYS BLUE!'))
const basic2 = delayedRetry(2, 1000, alwaysFail)

fork(basic2)

// Fetching URLs with retries
const fetchUrl = url =>
  new Task((rej, res) =>
    fetch(url)
      .then(r => res(`[${r.status}] ${r.statusText}`))
      .catch(rej))

const npm = delayedRetry(3, 1000, () => fetchUrl('http://www.npmjs.com/'))
fork(npm)

// since the function is curried we can also do this
const withRetries = delayedRetry(3)
const withDelayedRetries = withRetries(1000)
const npm2 = withDelayedRetries(() => fetchUrl('http://www.npmjs.com/'))
const google = withDelayedRetries(() => fetchUrl('http://www.google.com/'))
fork(npm2)
fork(google)

// Custom delay function
const delay = attemptNo =>
  attemptNo * 1000 // attemptNo is always >= 1

const withCustomDelayedRetries = withRetries(delay)
const npm3 = withCustomDelayedRetries(() => fetchUrl('http://www.npmjs.com'))
fork(npm3)