fetch-retry-ts

!Build and Test CI

Adds retry functionality to fetch().

Installation

``bash
npm install fetch-retry-ts
`

Usage

`typescript
import originalFetch from 'isomorphic-fetch';
import fetchBuilder from 'fetch-retry-ts';

const options = {
retries: 3,
retryDelay: 1000,
retryOn: [419, 503, 504],
};

const fetch = fetchBuilder(originalFetch, options);

fetch('https://example.com/').then(/ ... /);
`

fetch-retry-ts exports a function, which is used to build the new fetch()-compatible function supporting the retry logic.
It accepts two arguments:
* fetch (required): the original fetch() function (from isomorphic-fetch etc)
* defaults (optional): default values for the retry logic:
* retries?: number: number of attempts to make (3 by default);
* retryDelay?: number | () => number | (attempt: number, error: Error | null, response: Response | null) => number: delay between attempts (in ms). If specified as a function, the function accepts the following parameters:
* attempt: the number of the current attempt;
* error: Error object coming from fetch() when it rejects on a network failure, or null;
* response: Response or null if error !== null
It should return an integer, which is treated as the delay in ms before the enxt attempt is made. The default value for retryDelay is 1000.
retryOn?: number[] | (attempt: number, retries: number, error: Error | null, response: Response | null) => boolean: if specified as an array of integers, it is treated as a list of HTTP codes which trigger retry. When specified as a function, that functoin accepts the same parameters as the one described in retryDelay, and an additional parameter called retries, whcih is the number of configured retries. The function should return a truthy value if the request should be retried. If retryOn is a function, retries is ignored.* The default value for retryOn in [429, 503, 504].
It returns a function to be used instead of fetch().

The returned function accepts the same arguments as fetch(input: RequestInfo, init?: RequestInit), and three additional properties in init object. Those are retries, retryDelay, and retryOn.

Examples

$3

`typescript
fetch(url, {
retryOn: (attempt: number, retries: number, error: Error | null, response: Response | null): boolean => (
attempt < retries && (!!error || !response || response.status >= 500)
),
}).then(/ ... /)
`

$3

`typescript
fetch(url, {
retryOn: [],
}).then(/ ... /)
`

$3

`typescript
fetch(url, {
retryOn: (attempt: number, retries: number, error: Error | null, response: Response | null): boolean => (
attempt < retries && error === null / && additional logic to check response code /
),
}).then(/ ... /)
`

$3

`typescript
fetch(url, {
retryDelay: (attempt: number, error: Error | null, response: Response | null): number => (
Math.pow(2, attempt) * 1000
),
}).then(/ ... /)
``