p-retry

What is p-retry?

The p-retry package is a utility module that allows you to retry a promise-returning or async function. It is useful for handling operations that may fail due to transient errors and can be retried successfully after a short delay. This package provides a simple API to manage the number of retries, the delay between retries, and the condition for retrying.

What are p-retry's main functionalities?

Basic retry functionality

This code sample demonstrates how to use p-retry to attempt a function that returns a promise up to 5 times before giving up and throwing an error.

const pRetry = require('p-retry');

const runOperation = () => {
  return new Promise((resolve, reject) => {
    // Your operation here, e.g., a fetch request
    if (Math.random() > 0.5) {
      resolve('Success!');
    } else {
      reject(new Error('Failed!'));
    }
  });
};

pRetry(runOperation, {retries: 5}).then(result => console.log(result)).catch(error => console.error(error));

Custom retry options

This code sample shows how to provide custom retry options such as the number of retries, the backoff factor, and the minimum and maximum timeout between retries. It also demonstrates how to log information about failed attempts.

const pRetry = require('p-retry');

const runOperation = async () => {
  // Your async operation here
};

const onFailedAttempt = error => {
  console.log(`Attempt ${error.attemptNumber} failed. There are ${error.retriesLeft} retries left.`);
};

const options = {
  onFailedAttempt,
  retries: 3,
  factor: 2,
  minTimeout: 1000,
  maxTimeout: 5000
};

pRetry(runOperation, options).catch(error => console.error(error));

Conditional retry

This code sample illustrates how to use p-retry with a conditional check to determine whether to retry the operation based on the type of error encountered. If the error is not an instance of a specific error class, the retry is aborted.

const pRetry = require('p-retry');

const runOperation = async () => {
  // Your async operation here
};

const shouldRetry = error => error instanceof SpecificError;

pRetry(runOperation, { retries: 5, onFailedAttempt: error => {
  if (!shouldRetry(error)) {
    throw new pRetry.AbortError(error);
  }
}}).catch(error => console.error(error));

Other packages similar to p-retry

retry

The 'retry' package provides similar functionality to p-retry, allowing you to retry asynchronous functions. It is more low-level and does not return promises, which means it can be more flexible but also requires more boilerplate code to handle asynchronous operations.

async-retry

The 'async-retry' package is another alternative that offers a similar API to p-retry. It supports both promise-returning and async functions and provides options to customize retry strategies. It is comparable to p-retry but has its own syntax and options for configuration.

retry-as-promised

The 'retry-as-promised' package is designed to work with promises and provides a mechanism to retry a promise a certain number of times. It is similar to p-retry but has a different API and may offer different options for configuring retries.

README

p-retry

Retry a promise-returning or async function

It does exponential backoff and supports custom retry strategies for failed operations.

Install

npm install p-retry

Usage

import pRetry, {AbortError} from 'p-retry';
import fetch from 'node-fetch';

const run = async () => {
	const response = await fetch('https://sindresorhus.com/unicorn');

	// Abort retrying if the resource doesn't exist
	if (response.status === 404) {
		throw new AbortError(response.statusText);
	}

	return response.blob();
};

console.log(await pRetry(run, {retries: 5}));

API

pRetry(input, options?)

Returns a Promise that is fulfilled when calling input returns a fulfilled promise. If calling input returns a rejected promise, input is called again until the maximum number of retries is reached. It then rejects with the last rejection reason.

It does not retry on most TypeError's, with the exception of network errors. This is done on a best case basis as different browsers have different messages to indicate this. See whatwg/fetch#526 (comment)

input

Type: Function

Receives the current attempt number as the first argument and is expected to return a Promise or any value.

options

Type: object

Options are passed to the retry module.

onFailedAttempt(error)

Type: Function

Callback invoked on each retry. Receives the error thrown by input as the first argument with properties attemptNumber and retriesLeft which indicate the current attempt number and the number of attempts left, respectively.

import pRetry from 'p-retry';

const run = async () => {
	const response = await fetch('https://sindresorhus.com/unicorn');

	if (!response.ok) {
		throw new Error(response.statusText);
	}

	return response.json();
};

const result = await pRetry(run, {
	onFailedAttempt: error => {
		console.log(`Attempt ${error.attemptNumber} failed. There are ${error.retriesLeft} retries left.`);
		// 1st request => Attempt 1 failed. There are 4 retries left.
		// 2nd request => Attempt 2 failed. There are 3 retries left.
		// …
	},
	retries: 5
});

console.log(result);

The onFailedAttempt function can return a promise. For example, you can do some async logging:

import pRetry from 'p-retry';
import logger from './some-logger';

const run = async () => { … };

const result = await pRetry(run, {
	onFailedAttempt: async error => {
		await logger.log(error);
	}
});

If the onFailedAttempt function throws, all retries will be aborted and the original promise will reject with the thrown error.

shouldRetry(error)

Type: Function

Decide if a retry should occur based on the error. Returning true triggers a retry, false aborts with the error.

It is not called for TypeError (except network errors) and AbortError.

import pRetry from 'p-retry';

const run = async () => { … };

const result = await pRetry(run, {
	shouldRetry: error => !(error instanceof CustomError);
});

In the example above, the operation will be retried unless the error is an instance of CustomError.

signal

Type: AbortSignal

You can abort retrying using AbortController.

import pRetry from 'p-retry';

const run = async () => { … };
const controller = new AbortController();

cancelButton.addEventListener('click', () => {
	controller.abort(new Error('User clicked cancel button'));
});

try {
	await pRetry(run, {signal: controller.signal});
} catch (error) {
	console.log(error.message);
	//=> 'User clicked cancel button'
}

AbortError(message)

AbortError(error)

Abort retrying and reject the promise.

message

Type: string

An error message.

error

Type: Error

A custom error.

Tip

You can pass arguments to the function being retried by wrapping it in an inline arrow function:

import pRetry from 'p-retry';

const run = async emoji => {
	// …
};

// Without arguments
await pRetry(run, {retries: 5});

// With arguments
await pRetry(() => run('🦄'), {retries: 5});

Related

• p-timeout - Timeout a promise after a specified amount of time
• More…