@humanwhocodes/retry

What is @humanwhocodes/retry?

@humanwhocodes/retry is an npm package designed to simplify the process of retrying asynchronous operations. It provides a flexible and configurable way to handle retries, making it easier to manage operations that may fail intermittently, such as network requests or database queries.

What are @humanwhocodes/retry's main functionalities?

Basic Retry

This feature allows you to retry a function a specified number of times if it fails. In this example, the `fetchData` function is retried up to 5 times until it succeeds.

const { retry } = require('@humanwhocodes/retry');

async function fetchData() {
  // Simulate a function that may fail
  if (Math.random() < 0.7) {
    throw new Error('Fetch failed');
  }
  return 'Data fetched successfully';
}

retry(fetchData, { retries: 5 })
  .then(result => console.log(result))
  .catch(error => console.error(error));

Exponential Backoff

This feature allows you to implement exponential backoff, where the wait time between retries increases exponentially. In this example, the `fetchData` function is retried up to 5 times with an increasing delay between each retry.

const { retry } = require('@humanwhocodes/retry');

async function fetchData() {
  if (Math.random() < 0.7) {
    throw new Error('Fetch failed');
  }
  return 'Data fetched successfully';
}

retry(fetchData, { retries: 5, factor: 2, minTimeout: 1000 })
  .then(result => console.log(result))
  .catch(error => console.error(error));

Custom Retry Logic

This feature allows you to define custom retry logic by providing a `shouldRetry` function. In this example, the `shouldRetry` function logs each failed attempt and always returns true to continue retrying.

const { retry } = require('@humanwhocodes/retry');

async function fetchData() {
  if (Math.random() < 0.7) {
    throw new Error('Fetch failed');
  }
  return 'Data fetched successfully';
}

retry(fetchData, {
  retries: 5,
  shouldRetry: (error, attempt) => {
    console.log(`Attempt ${attempt} failed: ${error.message}`);
    return true;
  }
})
  .then(result => console.log(result))
  .catch(error => console.error(error));

Other packages similar to @humanwhocodes/retry

retry

The `retry` package provides a similar functionality for retrying operations with customizable options. It supports exponential backoff and custom retry strategies. Compared to @humanwhocodes/retry, it offers a more extensive set of configuration options and is widely used in the community.

promise-retry

The `promise-retry` package is designed for retrying promise-based operations. It supports custom retry strategies and exponential backoff. It is similar to @humanwhocodes/retry but focuses specifically on promise-based workflows, making it a good choice for modern JavaScript applications.

async-retry

The `async-retry` package provides a simple and flexible way to retry asynchronous operations. It supports custom retry strategies, exponential backoff, and is compatible with both promises and async/await. It is similar to @humanwhocodes/retry but offers a more concise API and is widely adopted in the community.

README

Retry utility

by Nicholas C. Zakas

If you find this useful, please consider supporting my work with a donation or nominate me for a GitHub Star.

Description

A utility for retrying failed async JavaScript calls based on the error returned.

Usage

Node.js

Install using npm or yarn:

npm install @humanwhocodes/retry

# or

yarn add @humanwhocodes/retry

Import into your Node.js project:

// CommonJS
const { Retrier } = require("@humanwhocodes/retry");

// ESM
import { Retrier } from "@humanwhocodes/retry";

Deno

Install using JSR:

deno add @humanwhocodes/retry

#or

jsr add @humanwhocodes/retry

Then import into your Deno project:

import { Retrier } from "@humanwhocodes/retry";

Bun

Install using this command:

bun add @humanwhocodes/retry

Import into your Bun project:

import { Retrier } from "@humanwhocodes/retry";

Browser

It's recommended to import the minified version to save bandwidth:

import { Retrier } from "https://cdn.skypack.dev/@humanwhocodes/retry?min";

However, you can also import the unminified version for debugging purposes:

import { Retrier } from "https://cdn.skypack.dev/@humanwhocodes/retry";

API

After importing, create a new instance of Retrier and specify the function to run on the error. This function should return true if you want the call retried and false if not.

// this instance will retry if the specific error code is found
const retrier = new Retrier(error => {
    return error.code === "ENFILE" || error.code === "EMFILE";
});

Then, call the retry() method around the function you'd like to retry, such as:

import fs from "fs/promises";

const retrier = new Retrier(error => {
    return error.code === "ENFILE" || error.code === "EMFILE";
});

const text = await retrier.retry(() => fs.readFile("README.md", "utf8"));

The retry() method will either pass through the result on success or wait and retry on failure. Any error that isn't caught by the retrier is automatically rejected so the end result is a transparent passing through of both success and failure.

Setting a Timeout

You can control how long a task will attempt to retry before giving up by passing the timeout option to the Retrier constructor. By default, the timeout is one minute.

import fs from "fs/promises";

const retrier = new Retrier(error => {
    return error.code === "ENFILE" || error.code === "EMFILE";
}, { timeout: 100_000 });

const text = await retrier.retry(() => fs.readFile("README.md", "utf8"));

When a call times out, it rejects the first error that was received from calling the function.

Setting a Concurrency Limit

When processing a large number of function calls, you can limit the number of concurrent function calls by passing the concurrency option to the Retrier constructor. By default, concurrency is 1000.

import fs from "fs/promises";

const retrier = new Retrier(error => {
    return error.code === "ENFILE" || error.code === "EMFILE";
}, { concurrency: 100 });

const filenames = getFilenames();
const contents = await Promise.all(
    filenames.map(filename => retrier.retry(() => fs.readFile(filename, "utf8"))
);

Aborting with AbortSignal

You can also pass an AbortSignal to cancel a retry:

import fs from "fs/promises";

const controller = new AbortController();
const retrier = new Retrier(error => {
    return error.code === "ENFILE" || error.code === "EMFILE";
});

const text = await retrier.retry(
    () => fs.readFile("README.md", "utf8"),
    { signal: controller.signal }
);

Developer Setup

1. Fork the repository
2. Clone your fork
3. Run npm install to setup dependencies
4. Run npm test to run tests

Debug Output

Enable debugging output by setting the DEBUG environment variable to "@hwc/retry" before running.

License

Apache 2.0

Prior Art

This utility is inspired by, and contains code from graceful-fs.