jeff3dx / promise-poll

Poll an asynchronous operation that is itself a Promise

Promise Poll

It's easy to poll based on the result of a predicate function, but what about Promises?

Promises return immediately and only "resolve" later. How can you poll a Promise operation without it returning immediately and end up with hundreds of unresolved Promises on the stack? Save time figuring this out by using promisePoll!

##Install npm install https://github.com/jeff3dx/promise-poll --save

Usage

import { promisePoll } from 'promise-poll';

promisePoll(targetPromiseFn, intervalMs, timeoutMs)
  .then(function(result) { 
    // todo after polling stops 
  });

targetPromiseFn

Function that returns a Promise. The Promise should perform your asynchronous operation (AJAX, etc.) and resolve either truthy or falsy.

• If it resolves truthy polling will stop.
• If it resolve falsy polling will continue.

intervalMs

Idle time to wait between each poll. Duration of the async operation itself is not counted.

timeoutMs

Duration after which polling will stop regardless of the asynch operation result. Will not interupt a poll in progress.

return value

Returns a Promise. When polling is done promisePoll will resolve itself with the data from the target promise.

You can resolve complex data. Just resolve either your data (truthy ) or null (falsy).

Example

(see example.js):

import { promisePoll } from 'promise-poll';
var ONE_SECOND = 1000;
var TEN_SECONDS = 10000;

function main() {

  // Declare a function that returns a Promise. promisePull() takes
  // a function that returns a Promose like this one:
  var asynchThing = function () {
    return new Promise(function (resolve, reject) {
      setTimeout(function () {
        // Decide to resolve truthy or falsy
        var result = Math.random() > 0.7;
        resolve(result);
      }, ONE_SECOND);
    });
  };

  var timeout = Date.now() + TEN_SECONDS;

  // promisePoll() will do the looping and run the async operation many
  // times until it resolves truthy or reaches the timeout
  promisePoll(asynchThing, ONE_SECOND, timeout)
    .then(function (result) {
      console.log('Polling done. Result: ' + result);
    });
}