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# exponential-backoff
A utility that allows retrying a function with an exponential delay between attempts.
## Installation
```
npm i exponential-backoff
```
## Usage
The `backOff<T>` function takes a promise-returning function to retry, and an optional `BackOffOptions` object. It returns a `Promise<T>`.
```ts
function backOff<T>(
request: () => Promise<T>,
options?: BackOffOptions
): Promise<T>;
```
Here is an example retrying a function that calls a hypothetical weather endpoint:
```js
import { backOff } from "exponential-backoff";
function getWeather() {
return fetch("weather-endpoint");
}
async function main() {
try {
const response = await backOff(() => getWeather());
// process response
} catch (e) {
// handle error
}
}
main();
```
Migrating across major versions? Here are our [breaking changes](https://github.com/coveo/exponential-backoff/tree/master/doc/migration-guide.md).
### `BackOffOptions`
- `delayFirstAttempt?: boolean`
Decides whether the `startingDelay` should be applied before the first call. If `false`, the first call will occur without a delay.
Default value is `false`.
- `jitter?: JitterType | string`
Decides whether a [jitter](https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/) should be applied to the delay. Possible values are `full` and `none`.
Default value is `none`.
- `maxDelay?: number`
The maximum delay, in milliseconds, between two consecutive attempts.
Default value is `Infinity`.
- `numOfAttempts?: number`
The maximum number of times to attempt the function.
Default value is `10`.
Minimum value is `1`.
- `retry?: (e: any, attemptNumber: number) => boolean | Promise<boolean>`
The `retry` function can be used to run logic after every failed attempt (e.g. logging a message, assessing the last error, etc.). It is called with the last error and the upcoming attempt number. Returning `true` will retry the function as long as the `numOfAttempts` has not been exceeded. Returning `false` will end the execution.
Default value is a function that always returns `true`.
- `startingDelay?: number`
The delay, in milliseconds, before executing the function for the first time.
Default value is `100` ms.
- `timeMultiple?: number`
The `startingDelay` is multiplied by the `timeMultiple` to increase the delay between reattempts.
Default value is `2`.
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