Retry utility

by Nicholas C. Zakas

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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:

1// CommonJS
2const { Retrier } = require("@humanwhocodes/retry");
3
4// ESM
5import { Retrier } from "@humanwhocodes/retry";

Deno

Install using JSR:

1deno add @humanwhocodes/retry
2
3#or
4
5jsr add @humanwhocodes/retry

Then import into your Deno project:

1import { Retrier } from "@humanwhocodes/retry";

Bun

Install using this command:

bun add @humanwhocodes/retry

Import into your Bun project:

1import { Retrier } from "@humanwhocodes/retry";

Browser

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

1import { Retrier } from "https://cdn.skypack.dev/@humanwhocodes/retry?min";

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

1import { 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.

1// this instance will retry if the specific error code is found
2const retrier = new Retrier(error => {
3    return error.code === "ENFILE" || error.code === "EMFILE";
4});

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

1import fs from "fs/promises";
2
3const retrier = new Retrier(error => {
4    return error.code === "ENFILE" || error.code === "EMFILE";
5});
6
7const 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.

1import fs from "fs/promises";
2
3const retrier = new Retrier(error => {
4    return error.code === "ENFILE" || error.code === "EMFILE";
5}, { timeout: 100_000 });
6
7const 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.

1import fs from "fs/promises";
2
3const retrier = new Retrier(error => {
4    return error.code === "ENFILE" || error.code === "EMFILE";
5}, { concurrency: 100 });
6
7const filenames = getFilenames();
8const contents = await Promise.all(
9    filenames.map(filename => retrier.retry(() => fs.readFile(filename, "utf8"))
10);

Aborting with AbortSignal

You can also pass an AbortSignal to cancel a retry:

1import fs from "fs/promises";
2
3const controller = new AbortController();
4const retrier = new Retrier(error => {
5    return error.code === "ENFILE" || error.code === "EMFILE";
6});
7
8const text = await retrier.retry(
9    () => fs.readFile("README.md", "utf8"),
10    { signal: controller.signal }
11);

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.