p-filter

What is p-filter?

The p-filter npm package is a utility that allows you to filter collections of items using asynchronous predicate functions. It is particularly useful when you need to perform some asynchronous operation to determine whether an item should be included in the resulting array.

What are p-filter's main functionalities?

Asynchronous Filtering

This feature allows you to filter an array asynchronously. The `getIsAnimal` function might perform an asynchronous operation, such as fetching data from an API to determine if the name belongs to an animal. The `pFilter` function will then return a new array containing only the names that are animals.

const pFilter = require('p-filter');
const getIsAnimal = async (name) => { /* ... */ };
const names = ['Sphinx', 'Hydra', 'Human'];
const animals = await pFilter(names, getIsAnimal);

Other packages similar to p-filter

async.filter

Part of the 'async' utility module, this function offers asynchronous filtering capabilities. It is part of a larger suite of asynchronous control flow and collection processing utilities, which might make it a heavier dependency than p-filter if only filtering is needed.

bluebird

Bluebird is a comprehensive promise library that includes a method called 'filter', which can be used for asynchronous filtering. It is more feature-rich than p-filter but also larger in size, which might be an overkill for simple use cases.

README

p-filter

Filter promises concurrently

Useful when you need to run promise-returning & async functions multiple times with different inputs concurrently and get a filtered down result.

Install

npm install p-filter

Usage

import pFilter from 'p-filter';
import getWeather from 'get-weather'; // Not a real module

const places = [
	getCapital('Norway').then(info => info.name),
	'Bangkok, Thailand',
	'Berlin, Germany',
	'Tokyo, Japan',
];

const filterer = async place => {
	const weather = await getWeather(place);
	return weather.temperature > 30;
};

const result = await pFilter(places, filterer);

console.log(result);
//=> ['Bangkok, Thailand']

API

pFilter(input, filterer, options?)

Returns a Promise that is fulfilled when all promises in input and ones returned from filterer are fulfilled, or rejects if any of the promises reject. The fulfilled value is an Array of the fulfilled values returned from filterer in input order.

input

Type: Iterable<Promise<unknown> | unknown>

Iterated over concurrently in the filterer function.

filterer(element, index)

Type: Function

The filterer function that decides whether an element should be included into result. Expected to return boolean | Promise<boolean>.

options

Type: object

See the p-map options.

concurrency

Type: number
Default: Infinity
Minimum: 1

The number of concurrently pending promises returned by filterer.

pFilterIterable(iterable, filterer, options?)

Returns an async iterable that iterates over the promises in iterable and ones returned from filterer concurrently, calling filterer for each element.

import {pFilterIterable} from 'p-filter';
import getWeather from 'get-weather'; // Not a real module

async function * getPlaces() {
	const name = await getCapital('Norway');

	yield name;
	yield 'Bangkok, Thailand';
	yield 'Berlin, Germany';
	yield 'Tokyo, Japan';
}

const places = getPlaces();

const filterer = async place => {
	const weather = await getWeather(place);
	return weather.temperature > 30;
};

for await (const element of pFilterIterable(places, filterer)) {
	console.log(element);
}
//=> ['Bangkok, Thailand']

iterable

Type: Iterable<Promise<unknown> | unknown>

Iterated over concurrently in the filterer function.

filterer(element, index)

Type: Function

The filterer function that decides whether an element should be included into result. Expected to return boolean | Promise<boolean>.

options

Type: object

See the p-map options.

concurrency

Type: number
Default: Infinity
Minimum: 1

The number of concurrently pending promises returned by filterer.

Related

• p-locate - Get the first fulfilled promise that satisfies the provided testing function
• p-map - Map over promises concurrently
• p-times - Run promise-returning & async functions a specific number of times concurrently
• More…