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Retry a promise-returning or async function
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readme.md

p-retry Build Status

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

const pRetry = require('p-retry');
const fetch = require('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 pRetry.AbortError(response.statusText);
	}

	return response.blob();
};

(async () => {
	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 doesn't retry on TypeError as that's a user error.

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.

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

	if (response.status !== 200) {
		throw new Error(response.statusText);
	}

	return response.json();
};

(async () => {
	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, to add a delay:

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

const run = async () => { ... };

(async () => {
	const result = await pRetry(run, {
		onFailedAttempt: async error => {
			console.log('Waiting for 1 second before retrying');
			await delay(1000);
		}
	});
})();

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

pRetry.AbortError(message)

pRetry.AbortError(error)

Abort retrying and reject the promise.

message

Type: string

Error message.

error

Type: Error

Custom error.

Tip

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

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

const run = async emoji => {
	//
};

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

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

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