Code Explainers

Browse the library

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
go 
package handlers
 
import (
	"net/http"

Cookie-based sessions in Gin

authentication cookies middleware
Intermediate 7 steps
python 
from pathlib import Path
 
 
def print_tree(root, prefix="", show_hidden=False):

Printing a directory tree with recursion

recursion filesystem sorting
Intermediate 6 steps
php 
<?php
 
namespace App\Http\Controllers\Auth;
 

How a Laravel registration endpoint works

validation database-transactions events
Intermediate 8 steps
ruby 
module LogParser
  class AccessLogStreamer
    SEVERITY_PATTERN = /\b(ERROR|WARN|FATAL)\b/
 

Streaming log lines with a Ruby enumerator

enumerators lazy-iteration regex-matching
Intermediate 6 steps
java 
@RestController
@RequestMapping("/webhooks/stripe")
public class StripeWebhookController {
 

How a Stripe webhook controller works in Spring

webhooks signature-verification event-handling
Intermediate 7 steps
typescript 
import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable, throwError, timer } from 'rxjs';
import { mergeMap, retryWhen } from 'rxjs/operators';

Exponential backoff retries in Angular

retry exponential-backoff rxjs
Advanced 7 steps
javascript 
import Papa from 'papaparse';
 
const MAX_SIZE = 5 * 1024 * 1024;
 

Validating and parsing CSV uploads in the browser

promises csv-parsing validation
Intermediate 8 steps
go 
package validators
 
import (
	"regexp"

Custom validators in Gin

validation sync.once regexp
Intermediate 5 steps
python 
from dataclasses import dataclass, fields, MISSING
from typing import get_type_hints, get_origin, get_args, Union
 
 

Type-checking dataclasses at runtime

dataclasses type-hints runtime-validation
Advanced 8 steps
rust 
use axum::{
    body::Body,
    extract::Request,
    http::{header::HeaderValue, HeaderName},

Request ID middleware in Axum

middleware tracing request-extensions
Intermediate 7 steps
php 
<?php
 
namespace App\Http\Controllers;
 

Handling avatar uploads in Laravel

file-upload image-processing validation
Intermediate 8 steps
ruby 
class HostnameValidator < ActiveModel::EachValidator
  MAX_LENGTH = 253
  LABEL = /\A(?!-)[a-z0-9-]{1,63}(?<!-)\z/i
 

Writing a custom hostname validator in Rails

validation custom validator regex
Intermediate 8 steps
ruby 
class PaymentsController < ApplicationController
  before_action :require_idempotency_key
 
  def create

Idempotent payment creation in Rails

idempotency transactions race-conditions
Advanced 10 steps
ruby 
class Survey < ApplicationRecord
  has_many :questions, dependent: :destroy
  has_many :respondents, dependent: :nullify
 

Nested survey forms in Rails

nested-attributes validations associations
Intermediate 9 steps
php 
<?php
 
namespace App\Security;
 

Secure password hashing with Argon2id in PHP

password-hashing argon2id timing-attacks
Intermediate 8 steps
python 
import time
import threading
 
 

How a thread-safe token bucket rate limiter works

rate-limiting concurrency locking
Intermediate 6 steps
go 
package logfmt
 
import (
	"bytes"

Pooling buffers for logfmt encoding in Go

object-pooling memory-reuse serialization
Intermediate 8 steps