Wait and retry in Nodejs

Oct 17, 2022

In other programming languages such as Java, Ruby and Python, there are Thread.sleep(), sleep, and time.sleep() methods to pause the execution of the current thread and wait after specified time to continue the execution, and when used together with loops, it can help address race condition issues for example. In node.js, and generally JavaScript, the way to pause and wait may not seem very obvious and frequently seen due to the nature of single-threaded, event-driven, and asyncronous architecture. However, since the use of wait and retry is still needed and helpful under certain circumstances, it is possible to simulate similar functions and effects in nodejs or JavaScript.

How to simulate `sleep`/`wait` with `setTimeout`

with new Promise

const wait = ms => new Promise(resolve => setTimeout(resolve, ms));

with util.promisify

import util from 'node:util';

const wait = util.promisify(setTimeout);

How to implement `retry` with back-off

with recursive functions

const retry = async (fn, depth = 0, numRetries = 3) => {
  try {
    return await fn();
  } catch (e) {
    if (depth === numRetries) {
      throw e;
    }
    console.log('retry...');
    await wait(2 ** depth * 10);
  
    return retry(fn, depth + 1, numRetries);
  }
}

with for loops

const retry = async (fn, retryDelayMs = 100, numRetries = 3) => {
  for (let attempt = 0; attempt <= numRetries; attempt++) {
    try {
      return await fn();
    } catch (e) {
      if (attempt === numRetries) {
        throw e;
      }
      console.log('retry...');
      await wait(retryDelayMs);

      retryDelayMs *= 2;
    }
  }
}

until function returns truthy value

const retry = async (fn, retryDelayMs = 100, numRetries = 3) => {
  let result;
  for(let i = 0; i < numRetries; i++) {
    try {
      result = await fn();
    } catch (e) {
      // ignore errors
    }
    if(result) {
      return result;
    }
    console.log('retry...');
    await wait(retryDelayMs);

    retryDelayMs *= 2;
  }
  return result;
};