p-throttle

What is p-throttle?

The p-throttle npm package is used to throttle the execution of asynchronous functions. It allows you to limit the number of times a function can be called over a specified period, which is useful for rate-limiting API requests or controlling the flow of operations in a system.

What are p-throttle's main functionalities?

Basic Throttling

This feature allows you to throttle the execution of a function. In this example, the function can only be called twice per second.

const pThrottle = require('p-throttle');

const throttle = pThrottle({ limit: 2, interval: 1000 });

const throttled = throttle(async (index) => {
  console.log(index);
});

(async () => {
  for (let i = 0; i < 10; i++) {
    throttled(i);
  }
})();

Throttling with Promises

This feature demonstrates throttling with asynchronous functions that return promises. The function is throttled to execute once every two seconds.

const pThrottle = require('p-throttle');

const throttle = pThrottle({ limit: 1, interval: 2000 });

const throttled = throttle(async (index) => {
  return new Promise((resolve) => {
    setTimeout(() => {
      console.log(index);
      resolve();
    }, 1000);
  });
});

(async () => {
  for (let i = 0; i < 5; i++) {
    await throttled(i);
  }
})();

Other packages similar to p-throttle

bottleneck

Bottleneck is a powerful rate limiter that can be used to control the rate of asynchronous operations. It offers more advanced features like clustering and priority queues, making it more suitable for complex scenarios compared to p-throttle.

limiter

Limiter is another rate-limiting library that provides a simple way to limit the number of operations over a given time period. It is similar to p-throttle but offers a more straightforward API for basic use cases.

rate-limiter-flexible

Rate-limiter-flexible is a highly flexible rate-limiting library that supports various backends like Redis and MongoDB. It provides more configuration options and is suitable for distributed systems, offering more flexibility than p-throttle.

README

p-throttle

Throttle promise-returning & async functions

It also works with normal functions.

It rate-limits function calls without discarding them, making it ideal for external API interactions where avoiding call loss is crucial.

Install

npm install p-throttle

Usage

Here, the throttled function is only called twice a second:

import pThrottle from 'p-throttle';

const now = Date.now();

const throttle = pThrottle({
	limit: 2,
	interval: 1000
});

const throttled = throttle(async index => {
	const secDiff = ((Date.now() - now) / 1000).toFixed();
	return `${index}: ${secDiff}s`;
});

for (let index = 1; index <= 6; index++) {
	(async () => {
		console.log(await throttled(index));
	})();
}
//=> 1: 0s
//=> 2: 0s
//=> 3: 1s
//=> 4: 1s
//=> 5: 2s
//=> 6: 2s

API

pThrottle(options)

Returns a throttle function.

options

Type: object

Both the limit and interval options must be specified.

limit

Type: number

The maximum number of calls within an interval.

interval

Type: number

The timespan for limit in milliseconds.

strict

Type: boolean
Default: false

Use a strict, more resource intensive, throttling algorithm. The default algorithm uses a windowed approach that will work correctly in most cases, limiting the total number of calls at the specified limit per interval window. The strict algorithm throttles each call individually, ensuring the limit is not exceeded for any interval.

signal

Type: AbortSignal

Abort pending executions. When aborted, all unresolved promises are rejected with signal.reason.

import pThrottle from 'p-throttle';

const controller = new AbortController();

const throttle = pThrottle({
	limit: 2,
	interval: 1000,
	signal: controller.signal
});

const throttled = throttle(() => {
	console.log('Executing...');
});

await throttled();
await throttled();
controller.abort('aborted')
await throttled();
//=> Executing...
//=> Executing...
//=> Promise rejected with reason `aborted`

onDelay

Type: Function

Get notified when function calls are delayed due to exceeding the limit of allowed calls within the given interval. The delayed call arguments are passed to the onDelay callback.

Can be useful for monitoring the throttling efficiency.

In the following example, the third call gets delayed and triggers the onDelay callback:

import pThrottle from 'p-throttle';

const throttle = pThrottle({
	limit: 2,
	interval: 1000,
	onDelay: (a, b) => {
		console.log(`Reached interval limit, call is delayed for ${a} ${b}`);
	},
});

const throttled = throttle((a, b) => {
	console.log(`Executing with ${a} ${b}...`);
});

await throttled(1, 2);
await throttled(3, 4);
await throttled(5, 6);
//=> Executing with 1 2...
//=> Executing with 3 4...
//=> Reached interval limit, call is delayed for 5 6
//=> Executing with 5 6...

throttle(function_)

Returns a throttled version of function_.

function_

Type: Function

A promise-returning/async function or a normal function.

throttledFn.isEnabled

Type: boolean
Default: true

Whether future function calls should be throttled and count towards throttling thresholds.

throttledFn.queueSize

Type: number

The number of queued items waiting to be executed.

Related

• p-debounce - Debounce promise-returning & async functions
• p-limit - Run multiple promise-returning & async functions with limited concurrency
• p-memoize - Memoize promise-returning & async functions
• More…