try-for

A simple polling utility that executes a function for a specified time period until a truthy value is returned or the specified duration has passed.

Installation

npm install try-for

Usage

Promise

const tryFor = require('try-for');

let result;

setTimeout(() => {
  result = 'Fin';
}, 2000);

const checkResult = () => result;

tryFor(checkResult, 5000)
  .then(result => {
    if (result) {
      console.log(result);
    } else {
      console.log('No result')
    }
  });

Async/await

const tryFor = require('try-for');

let result;

setTimeout(() => {
  result = 'Fin';
}, 2000);

const checkResult = () => result;

(async function test() {
  const result = await tryFor(checkResult, 5000);

  if (result) {
    console.log(result);
  } else {
    console.log('No result');
  }
})();

API

tryFor(func, duration, [optional: ms])

func - A function that will be called each poll iteration. Return any truthy value to exit early and a non-truthy value to continue polling.

duration - How long (in milliseconds) the poll should stay active before giving up.

ms - Interval (in milliseconds) between polls. Default is every 100ms.

Examples

In these examples, we use local storage for our test. We begin with an empty local storage object, set a timer to create a new item 2 seconds after our code is executed, and immediately begin listening for our new item every 100ms for the next 5 seconds.

Promise

const tryFor = require('try-for');

// Remove existing local storage item(s)
localStorage.clear();

// In 2 seconds, create our 'test' local storage item
setTimeout(() => localStorage.setItem('test', '1234'), 2000);

// Begin polling local storage for item 'test'
// and continue for 5 seconds
tryFor(() => localStorage.getItem('test'), 5000)
  .then(result => {
    if (result) {
      console.log('Result found: ', result); // Result found: 1234
    } else {
      console.log('Result not found in specified time');
    }
  });

Async/await

const tryFor = require('try-for');

(async function test() {
  localStorage.clear();
  setTimeout(() => localStorage.setItem('test', '1234'), 2000);

  const result = await tryFor(() => localStorage.getItem('test'), 5000);

  if (result) {
    console.log('Result found: ', result); // Result found: 1234
  } else {
    console.log('Result not found in specified time');
  }
})();

With ms option

const tryFor = require('try-for');

localStorage.clear();
setTimeout(() => localStorage.setItem('test', '1234'), 2000);

// Poll every 5ms
tryFor(() => localStorage.getItem('test'), 5000, 5)
  .then(result => {
    if (result) {
      console.log('Result found: ', result); // Result found: 1234
    } else {
      console.log('Result not found in specified time');
    }
  });