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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
```
$ npm install p-retry
```
## Usage
```js
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.
Does not retry on most `TypeErrors`, 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
const run = async () => {
const response = await fetch('https://sindresorhus.com/unicorn');
if (!response.ok) {
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, you can do some async logging:
```js
const pRetry = require('p-retry');
const logger = require('./some-logger');
const run = async () => { … };
(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.
### 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:
```js
const pRetry = require('p-retry');
const run = async emoji => {
// …
};
(async () => {
// 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)

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