async-poll/README.md

<div align="center" style="text-align: center;">
  <h1 style="border-bottom: none;">async-poll</h1>

  <p>Advanced polling module with timeout and metrics collection</p>
</div>

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> Writing your own polling function can be difficult and hard to collect metrics about the polling. `asyncPoll` aims to solve those with modern JavaScript and advanced API. By leveraging `async...await`, asynchronous polling function has never been easier and [Performance Timing/ Timeline API][performance-timeline-api-url] is used to collect metrics about each polling in terms of the duration.
>
> 🛠 Please check if `Performance Timing/ Timeline API` is supported on your browser or Node.js environment.

## Table of contents <!-- omit in toc -->

- [Pre-requisites](#pre-requisites)
- [Install](#install)
- [Usage](#usage)
  - [TypeScript or native ES modules](#typescript-or-native-es-modules)
  - [Node.js](#nodejs)
  - [Browser](#browser)
    - [ES Modules](#es-modules)
    - [IIFE](#iife)
  - [Performance Timing/ Timeline API via `PerformanceObserver`](#performance-timing-timeline-api-via-performanceobserver)
- [API Reference](#api-reference)
  - [AsyncPollOptions](#asyncpolloptions)
  - [asyncPoll\<T\>(fn, conditionFn[, options])](#asyncpolltfn-conditionfn-options)
- [License](#license)

## Pre-requisites

- [Node.js][nodejs-url] >= 8.9.0
- [NPM][npm-url] >= 5.5.1 ([NPM][npm-url] comes with [Node.js][nodejs-url] so there is no need to install separately.)

## Install

```sh
# Install via NPM
$ npm install --save async-poll
```

## Usage

### TypeScript or native ES modules

```ts
interface NewsData {
  data: {
    news: object[];
    status: number;
  };
}

import asyncPoll from 'async-poll';

/** Fetch news from a mock URL */
const fn = async () => fetch('https://example.com/api/news').then(r => r.json());
/** Keep polling until the more than 100 `news` are received or `status` returns `complete` */
const conditionFn = (d: NewsData) => d.data.news.length > 100 || d.data.status === 'complete';
/** Poll every 2 seconds */
const interval = 2e3;
/** Timeout after 30 seconds and returns end result */
const timeout = 30e3;

asyncPoll<NewsData>(fn, conditionFn, { interval, timeout })
  .then(console.log)
  .catch(console.error);
```

### Node.js

```js
const { asyncPoll } = require('async-poll');

/** Fetch news from a mock URL */
const fn = async () => fetch('https://example.com/api/news').then(r => r.json());
/** Keep polling until the more than 100 `news` are received or `status` returns `complete` */
const conditionFn = d => d.data.news.length > 100 || d.data.status === 'complete';
/** Poll every 2 seconds */
const interval = 2e3;
/** Timeout after 30 seconds and returns end result */
const timeout = 30e3;

asyncPoll(fn, conditionFn, { interval, timeout })
  .then(console.log)
  .catch(console.error);
```

### Browser

#### ES Modules

```html
<script type="module">
  import { asyncPoll } from 'https://unpkg.com/async-poll@latest/dist/async-poll.js';

  /** Fetch news from a mock URL */
  const fn = async () => fetch('https://example.com/api/news').then(r => r.json());
  /** Keep polling until the more than 100 `news` are received or `status` returns `complete` */
  const conditionFn = d => d.data.news.length > 100 || d.data.status === 'complete';
  /** Poll every 2 seconds */
  const interval = 2e3;
  /** Timeout after 30 seconds and returns end result */
  const timeout = 30e3;

  asyncPoll(fn, conditionFn, { interval, timeout })
    .then(console.log)
    .catch(console.error);
</script>
```

#### IIFE

```html
<script src="https://unpkg.com/async-poll@latest/dist/async-poll.iife.js"></script>
<script>
  const { asyncPoll } = window.AsyncPoll;

  /** Fetch news from a mock URL */
  const fn = async () => fetch('https://example.com/api/news').then(r => r.json());
  /** Keep polling until the more than 100 `news` are received or `status` returns `complete` */
  const conditionFn = d => d.data.news.length > 100 || d.data.status === 'complete';
  /** Poll every 2 seconds */
  const interval = 2e3;
  /** Timeout after 30 seconds and returns end result */
  const timeout = 30e3;

  asyncPoll(fn, conditionFn, { interval, timeout })
    .then(console.log)
    .catch(console.error);
</script>
```

### Performance Timing/ Timeline API via `PerformanceObserver`

Performance timing data can be obtained via the experimental [Performance Tming API][performance-timing-api-url] that has been added as of [Node.js 8.5.0][nodejs-url] or [Performance Timeline API][performance-timeline-api-url] on browsers.

```ts
/** For Node.js **only**, no import is required on browser. */
import { PerformanceObserver } from 'perf_hooks';

async function main() {
  let measurements: Record<string, unknown> = {};
  const perfObs = new PerformanceObserver((list) => {
    for (const n of list.getEntries()) {
      measurements[n.name] = n.duration;
    }
  });
  perfObs.observe({ entryTypes: ['measure'] });
  const d = await asyncPoll(fn, conditionFn, { interval, timeout });
  perObs.disconnect();

  return {
    data: d,
    measurements,
  };
}
```

## API Reference

### AsyncPollOptions

```ts
interface AsyncPollOptions {
  interval: number;
  timeout: number;
}
```

### asyncPoll\<T\>(fn, conditionFn[, options])

- `fn` <[Function][function-mdn-url]> Function to execute for each polling happens.
- `conditionFn` <[Function][function-mdn-url]> Function to check the condition before a subsequent polling takes place. The function should return a boolean. If `true`, the polling stops and returns with a value in the type of `T`.
- `options` <[AsyncPollOptions][asyncpolloptions-url]> Polling options.
  - `interval` <[number][number-mdn-url]> Polling interval.
  - `timeout` <[number][number-mdn-url]> Timeout.
- returns: <[Promise][promise-mdn-url]<`T`>> Promise which resolves with a value in the type of `T`.

## License

[MIT License](https://motss.mit-license.org/) © Rong Sen Ng (motss)

<!-- References -->
[typescript-url]: https://github.com/Microsoft/TypeScript
[nodejs-url]: https://nodejs.org
[npm-url]: https://www.npmjs.com
[node-releases-url]: https://nodejs.org/en/download/releases
[performance-timing-api-url]: https://nodejs.org/api/perf_hooks.html
[performance-timeline-api-url]: https://developer.mozilla.org/en-US/docs/Web/API/Performance
[asyncpolloptions-url]: #asyncpolloptions

<!-- MDN -->
[array-mdn-url]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
[boolean-mdn-url]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean
[function-mdn-url]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function
[map-mdn-url]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map
[number-mdn-url]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number
[object-mdn-url]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object
[promise-mdn-url]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise
[regexp-mdn-url]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp
[set-mdn-url]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set
[string-mdn-url]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String

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