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https://github.com/sindresorhus/p-retry

Retry a promise-returning or async function
https://github.com/sindresorhus/p-retry

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Retry a promise-returning or async function

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# p-retry



> Retry a promise-returning or async function



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



## Install



```sh

npm install p-retry

```



## Usage



```js

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](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#Checking_that_the_fetch_was_successful) to indicate this. See [whatwg/fetch#526 (comment)](https://github.com/whatwg/fetch/issues/526#issuecomment-554604080)



#### 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`](https://github.com/tim-kos/node-retry#retryoperationoptions) 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.



```js

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:



```js

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`.



```js

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`](https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal)



You can abort retrying using [`AbortController`](https://developer.mozilla.org/en-US/docs/Web/API/AbortController).



```js

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:



```js

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](https://github.com/sindresorhus/p-timeout) - Timeout a promise after a specified amount of time

- [More…](https://github.com/sindresorhus/promise-fun)