simple-poll

A pull-based polling utility that allows you to poll any function that returns a promise with configurable delay.

Getting started

Install using npm:

npm install @alivenotions/simple-poll

Or with yarn:

yarn add @alivenotions/simple-poll

With a script tag:

<script src="https://unpkg.com/@alivenotions/simple-poll/dist/poll.umd.min.js"></script>

Support

• Works for Node >= 10
• Will work for older versions but polyfills are needed for async iterator and generators(core-js/modules/es7.symbol.async-iterator and regenerator-runtime/runtime).
• Works on all modern browsers. For older browsers polyfills are needed.

Create a polling object

The Poll function expects an object with three keys:

• delay: number, if not passed, a default of 0 is taken
• executor: a promise returning function, throws an error if not passed
• args: array of arguments to the executor function, if not passed, a default of an empty array is taken

const { Poll } = require('@alivenotions/simple-poll')
const fetch = require('node-fetch')

const poll = Poll({
  delay: 0,
  executor: fetch,
  args: ['https://jsonplaceholder.typicode.com/todos/1']
})

Alternatively, you can chain the values by calling the setters.

const { Poll } = require('@alivenotions/simple-poll')
const fetch = require('node-fetch')

const poll = Poll()
  .executor(fetch)
  .args(['https://jsonplaceholder.typicode.com/todos/1'])
  .delay(1000)

Subscription

The poll object is lazy and won't start polling until it is subscribed to. Subscription takes a callback function that is expecting the response as the argument. The unsubscribe handler stops the polling and takes in a callback which will run after unsubscription.

const { Poll } = require('@alivenotions/simple-poll')
const fetch = require('node-fetch')

const poll = Poll({
  delay: 0,
  executor: fetch,
  args: ['https://jsonplaceholder.typicode.com/todos/1']
})
const cb = response => response.json().then(console.log)

poll.subscribe(cb)

// alternatively, you can compose this
Poll()
  .executor(fetch)
  .args('https://jsonplaceholder.typicode.com/todos/1')
  .delay(1000)
  .subscribe(console.log)

// to unsubscribe
poll.unsubscribe(cb)

Error handling

The onError handler takes in a callback function that will run if the executor throws any error. The polling continues after that.

const poll = Poll({
  delay: 1000,
  executor: fetch,
  args: ['https://jsonplaceholder.typicode.com/todos/1'],
})
  .onError(err => console.error(err))
  .subscribe()

If no onError handler is passed then the error is propagated and polling is cancelled.

Modifying configuration

You can change the values of the polling object by using the following setters:

const addNumbers = (x, y) => new Promise(resolve => resolve(x + y))

poll.delay(5000)
poll.executor(addNumbers)
poll.args([1, 2])