Code Explainers
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javascript
function initScrollSpy() { const links = Array.from(document.querySelectorAll('.nav a[href^="#"]')); const sections = links .map((link) => document.querySelector(link.getAttribute('href')))
Building a scroll spy with IntersectionObserver
intersectionobserver
dom
event-driven
Intermediate
7 steps
rust
#[derive(Debug, Default)] pub struct RequestBuilder { url: String, method: String,
The builder pattern in Rust
builder-pattern
method-chaining
ergonomic-api
Intermediate
8 steps
java
package com.example.lb; import java.util.List; import java.util.concurrent.atomic.AtomicInteger;
A thread-safe round-robin load balancer in Java
concurrency
load-balancing
round-robin
Intermediate
9 steps
python
from typing import Callable, Dict, Type class PluginRegistry:
A decorator-based plugin registry in Python
decorators
registry pattern
factory
Intermediate
9 steps
typescript
import { Component, inject, effect } from '@angular/core'; import { FormControl, ReactiveFormsModule } from '@angular/forms'; import { ActivatedRoute, Router } from '@angular/router'; import { toSignal } from '@angular/core/rxjs-interop';
Debounced search that syncs to the URL in Angular
signals
reactive-forms
debouncing
Advanced
8 steps
ruby
namespace :counter_cache do desc "Recalculate comments_count for posts after a backfill" task warm_post_comments: :environment do scope = Post.where(comments_count: nil).or(Post.where("comments_count < 0"))
Backfilling counter caches in a Rake task in Rails
counter-cache
batching
rake-tasks
Intermediate
6 steps
go
package humanize import ( "fmt"
Parsing human-readable byte sizes in Go
parsing
regex
lookup-table
Intermediate
8 steps
ruby
class ToastBroadcaster include ActionView::RecordIdentifier def self.broadcast_to(user, message:, type: :notice)
How Turbo Stream toasts broadcast in Rails
turbo-streams
service-object
real-time
Intermediate
6 steps
typescript
import { NestFactory } from '@nestjs/core'; import { DocumentBuilder, SwaggerModule } from '@nestjs/swagger'; import { ValidationPipe } from '@nestjs/common'; import { ApiProperty } from '@nestjs/swagger';
Wiring validation and Swagger docs in NestJS
validation
openapi
decorators
Intermediate
8 steps
python
from fastapi import APIRouter, BackgroundTasks, Depends, HTTPException, status from pydantic import BaseModel, EmailStr from sqlalchemy.orm import Session
Building a signup endpoint in FastAPI
dependency-injection
request-validation
background-tasks
Intermediate
8 steps
javascript
const ROLE_PERMISSIONS = { admin: ['users:read', 'users:write', 'billing:read', 'billing:write'], manager: ['users:read', 'billing:read'], member: ['users:read'],
Role-based permissions middleware in Express
authorization
middleware
rbac
Intermediate
9 steps
rust
use axum::{extract::{Path, State}, http::StatusCode, Json}; use dashmap::DashMap; use serde::Serialize; use std::sync::Arc;
Request coalescing in an Axum handler
caching
concurrency
request-coalescing
Advanced
8 steps
java
public interface GitHubClient { @GetExchange("/users/{username}") GitHubUser getUser(@PathVariable String username);
Declarative HTTP clients in Spring
http-client
declarative-api
proxy
Intermediate
8 steps
php
<?php namespace App\Console\Commands;
Releasing stale document locks in Laravel
artisan-command
transactions
row-locking
Intermediate
6 steps
ruby
class TemplateInterpolator PLACEHOLDER = /\{\{\s*([\w.]+)\s*\}\}/ def initialize(strict: false)
Interpolating templates with dotted keys in Ruby
regex
string-interpolation
hash-traversal
Intermediate
6 steps
typescript
import { Component, Input } from '@angular/core'; interface Order { id: string;
How Angular ICU plurals localize an order summary
i18n
pluralization
standalone-component
Intermediate
8 steps
python
from django import forms from django.utils import timezone from .models import Reservation
Multi-field validation in a Django ModelForm
form validation
cross-field validation
modelform
Intermediate
7 steps
javascript
function attachThousandSeparators(input, { locale = 'en-US' } = {}) { const formatter = new Intl.NumberFormat(locale); const groupSep = formatter.format(11111).replace(/\d/g, '')[0] || ','; const decimalSep = formatter.format(1.1).replace(/\d/g, '')[0] || '.';
Live thousand separators without losing the caret
dom
intl
caret-preservation
Advanced
8 steps