ts-retryable

Given a function, creates a new function with built-in retry capabilities.

const lessFlaky = retryable(flaky, {shouldRetry: () => true})

Example

import { retryable } from 'ts-retryable'
import nodeFetch from "node-fetch";

export const myFetch = retryable(nodeFetch, {
   shouldRetry: ((count, error) => count < 3),
   delay: 5000
})
// Elsewhere, use this `myFetch` but get automatic retries.

In my code, the shouldRetry became fairly sophisticated, analyzing not only the retry count, but the details of the error that was thrown.

This will work with any async function, and I developed for an API-heavy app. Dropbox was one of the APIs, and here's more realistic, but simplified example:

// import dropboxApi ...
dropboxApi.filesDownload = makeRetryable(
   dropboxApi.filesDownload, 
   {
     shouldRetry: async function (count: number, e: DropboxResponse<files.FileMetadata>): Promise<boolean> {
         if (count >= 4) return false
         if (e.status === 401) {
            await client.refreshAccessToken()
            return true
          }
         return isNetworkError(e);
      },
     delay: 5000,
   })

I also used functional composition to produce a fetch that handled OAuth and network-induced errors.

Details

The retry capabilities are controlled by the options object provided:

• shouldRetry is a function you provide that determines whether a failure will retry. It receives the retry count (starting at 1), and the exception that was thrown/rejected, and returns true or false. Here are common examples:

  () => true                  // just keep trying (forever?)
  (c) => c <= 5               // 5 or fewer times
  (_, e) => e.status === 503  // on a specific error

  Note: Although this function is basically function asking for true/false, it is possible to execute other logic, including side effects. This could be any sort of "extra" logic to prepare for a retry.

• delay is how long to wait before retrying. By default, there is no delay. The value of delay is either a number (milliseconds) or a function. The function will receive the call count and exception thrown. Exponential backoff looks like (c) => Math.pow(2, c) * 1000. It's possible that the exception would be useful: the exception saying a server is busy may suggest a longer timeout than some intermittent exception.

Sync

This module assumes that the function will return a promise, as this will be 90% (or more) of the use cases. If you want to retry synchronous code, use retryableSync instead. It does not support any sort of delay, and shouldRetry should be sync as well. Failure for sync functions means throwing an exception, (and failure for Promise/async functions means returning a rejected promise).

Other Libs

Lots of these solutions are (1) not Typescript (2) function specific, such as fetch only. Feel free to try any of them.

• very similar: https://www.npmjs.com/package/as-retryable-promise
• https://github.com/jonbern/fetch-retry nice version
• https://www.chrisarmstrong.dev/posts/retry-timeout-and-cancel-with-fetch
• https://github.com/poetic/retryable-promise
• https://github.com/valeriangalliat/promise-retryable
• https://www.npmjs.com/package/keep-trying