Code Explainers

Browse the library

javascript 
import { useCallback, useState } from "react";
 
const MIN = 0;
const MAX = 1000;

Building a dual-thumb price slider in React

controlled-components state-clamping usecallback
Intermediate 8 steps
ruby 
class ProgressBar
  BAR_WIDTH = 40
 
  def initialize(total, io: $stdout)

Building a terminal progress bar in Ruby

state tracking terminal output time estimation
Intermediate 8 steps
typescript 
import { useState, useEffect, useRef, useCallback } from "react";
 
interface Suggestion {
  id: string;

A debounced autocomplete hook in React

debounce custom-hooks abortcontroller
Advanced 7 steps
java 
@Configuration
public class DataSourceLoggingConfig {
 
    @Bean

Wrapping a Spring DataSource for query tracing

proxy pattern observability data source
Intermediate 7 steps
go 
package handlers
 
type WebhookEvent struct {
	ID   string          `json:"id"`

Verifying and processing webhooks in Gin

webhooks hmac idempotency
Intermediate 9 steps
php 
<?php
 
namespace App\Services;
 

Idempotent role assignment in Laravel

many-to-many pivot-data idempotency
Intermediate 8 steps
rust 
use axum::body::Bytes;
use axum::http::{header, HeaderValue, StatusCode};
use axum::response::{IntoResponse, Response};
use serde::Serialize;

Custom Axum responses with per-user ETags

etag trait-implementation generics
Intermediate 7 steps
python 
import base64
import json
from typing import Annotated, Optional
 

Cursor pagination in a FastAPI endpoint

pagination cursor async
Intermediate 9 steps
javascript 
class LyricsSync {
  constructor(audio, container, lines) {
    this.audio = audio;
    this.container = container;

Building a synced lyrics highlighter

binary-search dom-manipulation event-handling
Intermediate 9 steps
typescript 
import { Body, Controller, Ip, Post, UnauthorizedException } from '@nestjs/common';
import { Throttle, ThrottlerGuard } from '@nestjs/throttler';
import { UseGuards } from '@nestjs/common';
import { AuthService } from './auth.service';

Rate-limiting an auth flow in NestJS

rate-limiting authentication guards
Intermediate 8 steps
java 
@RestController
@RequestMapping("/api/products")
@Validated
public class ProductSearchController {

Validating query params in a Spring controller

validation pagination rest-api
Intermediate 8 steps
php 
<?php
 
namespace App\Services;
 

Merging overlapping busy time blocks in PHP

interval-merging sorting datetime
Intermediate 8 steps
rust 
use axum::{extract::State, http::StatusCode, response::IntoResponse, Json};
use serde::{Deserialize, Serialize};
use std::sync::Arc;
 

Batch inserts with per-item status in Axum

batch-processing error-handling serde
Intermediate 8 steps
typescript 
import { Component, computed, DestroyRef, inject, input, output, signal } from '@angular/core';
import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
import { interval, map, takeWhile } from 'rxjs';
 

How a signal-driven countdown works in Angular

signals reactivity rxjs
Intermediate 8 steps
ruby 
class Product < ApplicationRecord
  scope :search, ->(query) {
    return all if query.blank?
 

Building a multi-term search scope in Rails

arel scopes full-text search
Advanced 7 steps
php 
<?php
 
namespace App\Listeners;
 

How event subscribers group listeners in Laravel

event-driven subscribers queues
Intermediate 6 steps
javascript 
const express = require('express');
 
const app = express();
 

Enforcing HTTPS with Express middleware

middleware https security
Intermediate 6 steps
rust 
use std::time::Duration;
 
#[derive(Debug, PartialEq)]
pub enum ParseDurationError {

Parsing duration strings safely in Rust

parsing error-handling checked-arithmetic
Intermediate 8 steps