Code Explainers

Code explainers tagged #async-await

javascript 
async function uploadInBatches(records, uploadFn, { batchSize = 100, concurrency = 3 } = {}) {
  const batches = [];
  for (let i = 0; i < records.length; i += batchSize) {
    batches.push(records.slice(i, i + batchSize));

Uploading records with bounded concurrency

concurrency worker-pool async-await
Advanced 8 steps
typescript 
export class Semaphore {
  private available: number;
  private readonly waiters: Array<() => void> = [];
 

Building an async Semaphore in TypeScript

concurrency async-await promises
Advanced 6 steps
typescript 
type Task<T> = () => Promise<T>;
 
export class Mutex {
  private queue: Array<() => void> = [];

Building an async mutex in TypeScript

concurrency promises locking
Advanced 7 steps
javascript 
const express = require('express');
const router = express.Router();
const db = require('../db');
 

Building a paginated articles endpoint in Express

pagination input-validation async-await
Intermediate 8 steps
javascript 
const express = require('express');
const router = express.Router();
 
router.get('/articles/:slug', async (req, res, next) => {

Content negotiation with res.format in Express

content-negotiation routing error-handling
Intermediate 9 steps
typescript 
interface PollOptions<T> {
  intervalMs?: number;
  timeoutMs?: number;
  signal?: AbortSignal;

A cancellable polling helper in TypeScript

polling async-await abortsignal
Intermediate 9 steps
javascript 
const asyncHandler = (fn) => (req, res, next) => {
  Promise.resolve(fn(req, res, next)).catch(next);
};
 

Async error handling in Express routes

async-await error-handling middleware
Intermediate 7 steps
javascript 
async function mapWithConcurrency(items, limit, worker) {
  const results = new Array(items.length);
  let nextIndex = 0;
 

Bounded-concurrency async map in JavaScript

concurrency async-await promises
Intermediate 7 steps
typescript 
type RetryOptions = {
  retries?: number;
  timeoutMs?: number;
  baseDelayMs?: number;

Retry with timeout and backoff in TypeScript

promises retry exponential-backoff
Intermediate 10 steps
typescript 
export function chunk<T>(items: readonly T[], size: number): T[][] {
  if (size <= 0 || !Number.isInteger(size)) {
    throw new RangeError(`chunk size must be a positive integer, got ${size}`);
  }

Splitting work into sequential batches in TypeScript

generics async-await batching
Intermediate 5 steps
javascript 
async function fetchAllPages(baseUrl, { pageSize = 100, headers = {} } = {}) {
  const results = [];
  let cursor = null;
 

Cursor-based pagination with fetch

pagination async-await fetch
Intermediate 6 steps
javascript 
async function pollJobUntilComplete(jobId, { interval = 2000, timeout = 60000, signal } = {}) {
  const deadline = Date.now() + timeout;
 
  while (true) {

Polling a job until it finishes in JavaScript

polling async-await abortsignal
Intermediate 6 steps