Code Explainers
Intermediate code explainers
typescript
import { useState, useCallback } from 'react'; type Todo = { id: string;
Optimistic UI updates in a React hook
optimistic-updates
custom-hooks
error-handling
Intermediate
8 steps
python
from flask import Blueprint, request, url_for, jsonify, abort from flask.views import MethodView from .models import Article, db
Building a paginated JSON API with Flask MethodView
rest-api
pagination
class-based-views
Intermediate
10 steps
java
public final class DeepCopier { private static final ObjectMapper MAPPER = new ObjectMapper() .registerModule(new JavaTimeModule())
Deep-copying objects via Jackson serialization
serialization
deep-copy
generics
Intermediate
7 steps
rust
use std::fs::File; use std::io::{self, Read}; use std::path::Path;
Streaming a SHA-256 hash of a file in Rust
hashing
buffered-io
streaming
Intermediate
5 steps
go
package fsutil import ( "io/fs"
Walking a directory tree to find large files in Go
filesystem
recursion
closures
Intermediate
7 steps
ruby
module DeepImmutable module_function def deep_freeze(obj)
Deep-freezing config with recursive immutability
immutability
recursion
deep-copy
Intermediate
8 steps
rust
use axum::{ extract::State, http::StatusCode, Json,
Idempotent webhook handling in Axum
deduplication
idempotency
shared-state
Intermediate
8 steps
php
<?php namespace App\Services;
Tagged cache invalidation in Laravel
caching
cache-tags
invalidation
Intermediate
5 steps
javascript
import { NextResponse } from 'next/server'; import { createWriteStream } from 'node:fs'; import { mkdir } from 'node:fs/promises'; import { pipeline } from 'node:stream/promises';
Streaming file uploads in a Next.js route
file-upload
streams
validation
Intermediate
9 steps
go
package middleware import ( "log"
Per-IP rate limiting middleware in Gin
rate-limiting
middleware
concurrency
Intermediate
8 steps
typescript
import { Component, ChangeDetectionStrategy, inject, signal } from '@angular/core'; import { CommonModule } from '@angular/common'; import { ScrollingModule } from '@angular/cdk/scrolling'; import { toObservable } from '@angular/core/rxjs-interop';
Virtual scrolling a contact list in Angular
virtual-scrolling
signals
change-detection
Intermediate
6 steps
java
package com.example.time; import java.time.Duration; import java.time.Instant;
Adding ISO-8601 durations across time zones in Java
date-time
iso-8601
parsing
Intermediate
7 steps
python
from urllib.parse import urlparse, parse_qs from dataclasses import dataclass, field ALLOWED_SCHEMES = {"http", "https"}
Validating URLs into a safe endpoint in Python
input validation
url parsing
dataclasses
Intermediate
7 steps
php
final class BitmapGrid { private SplFixedArray $cells;
A flat-array bitmap grid in PHP
data-structures
row-major-order
bitmap
Intermediate
7 steps
go
func handleUpload(w http.ResponseWriter, r *http.Request) { if err := r.ParseMultipartForm(32 << 20); err != nil { http.Error(w, "failed to parse form: "+err.Error(), http.StatusBadRequest) return
Handling multi-file uploads in Go
multipart
file-upload
http-handler
Intermediate
9 steps
typescript
import { Module } from '@nestjs/common'; import { TypeOrmModule } from '@nestjs/typeorm'; import { BullModule } from '@nestjs/bullmq';
How a NestJS feature module wires up
dependency-injection
modularity
orm
Intermediate
7 steps
python
from flask import Blueprint, render_template, request, redirect, url_for, flash from werkzeug.security import check_password_hash from .models import User, db
A change-email route in Flask
blueprints
form-validation
password-hashing
Intermediate
8 steps
ruby
class DatasetImportJob < ApplicationJob queue_as :default def perform(import)
Streaming import progress with a Rails job
background-jobs
turbo-streams
progress-tracking
Intermediate
9 steps