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- # p-retry [](https://travis-ci.org/sindresorhus/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}));
- })();
- ```
- With the `onFailedAttempt` option:
- ```js
- 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);
- })();
- ```
- ## 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 max retries are 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 number of attempts 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.
- ### pRetry.AbortError(message|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)
- ## License
- MIT © [Sindre Sorhus](https://sindresorhus.com)
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