Code Explainers
Browse the library
javascript
import { NextResponse } from 'next/server'; import { Redis } from '@upstash/redis'; const redis = Redis.fromEnv();
Sliding-window rate limiting in a Next.js route
rate-limiting
redis
sorted-set
Advanced
8 steps
python
from flask import Blueprint, jsonify from sqlalchemy import text from sqlalchemy.exc import SQLAlchemyError
Building a health check endpoint in Flask
health-check
blueprint
error-handling
Intermediate
6 steps
java
@Component public class RegionCacheWarmer implements SmartInitializingSingleton { private static final Logger log = LoggerFactory.getLogger(RegionCacheWarmer.class);
Warming a Spring cache at startup
caching
startup-hook
dependency-injection
Intermediate
7 steps
typescript
import { Controller, Param, Sse, MessageEvent } from '@nestjs/common'; import { Observable, interval, merge } from 'rxjs'; import { filter, map, takeWhile } from 'rxjs/operators'; import { JobService } from './job.service';
Streaming job progress with SSE in NestJS
server-sent-events
reactive-streams
rxjs
Intermediate
8 steps
go
package breaker import ( "errors"
How a circuit breaker works in Go
circuit-breaker
state-machine
concurrency
Intermediate
8 steps
php
<?php final class TaskProgressReporter {
Tracking task progress in a JSON file
state-persistence
atomic-writes
json
Intermediate
9 steps
ruby
class WebhookSignatureConstraint def initialize(provider) @provider = provider end
Verifying webhook signatures with Rails routing constraints
routing constraints
hmac
webhooks
Advanced
7 steps
rust
#[derive(Debug, Clone, PartialEq)] pub enum Token { Number(f64), Plus,
How a tokenizer turns text into tokens
lexing
enums
iterators
Intermediate
8 steps
javascript
const MAX_FILE_SIZE = 5 * 1024 * 1024; const ALLOWED_TYPES = { 'image/jpeg': ['jpg', 'jpeg'],
Validating file uploads by content, not just claims
input-validation
security
magic-bytes
Intermediate
7 steps
python
import pandas as pd import numpy as np
Cleaning a customer DataFrame with pandas
data-cleaning
regex
normalization
Intermediate
9 steps
java
public final class EmailNormalizer { private static final Pattern EMAIL_PATTERN = Pattern.compile( "^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}$"
Normalizing email addresses in Java
validation
regex
normalization
Intermediate
8 steps
typescript
import { Controller, All, Req,
Catch-all routes and error shaping in NestJS
exception-handling
routing
middleware
Intermediate
6 steps
ruby
module UniqueJob extend ActiveSupport::Concern class_methods do
Deduplicating Active Job enqueues in Rails
concurrency
idempotency
caching
Advanced
9 steps
rust
use axum::{ extract::{FromRequestParts, Host}, http::{request::Parts, StatusCode}, };
Multi-tenant DB routing in Axum extractors
multi-tenancy
extractors
connection-pooling
Advanced
8 steps
javascript
function zip(keys, values) { if (keys.length !== values.length) { throw new RangeError('zip expects arrays of equal length'); }
Three ways to zip arrays in JavaScript
arrays
higher-order-functions
pairing
Intermediate
6 steps
python
from datetime import date, timedelta from typing import Annotated from fastapi import APIRouter, Depends, Query
Validating date ranges with FastAPI dependencies
dependency-injection
validation
pydantic
Intermediate
6 steps
java
@RestController @RequestMapping("/api/products") @RequiredArgsConstructor public class ProductBatchController {
Batch JSON Merge Patch in Spring
json-merge-patch
rest-api
partial-update
Intermediate
8 steps
typescript
import { ArgumentsHost, Catch, ConflictException,
Turning TypeORM lock errors into 409s in NestJS
exception-handling
optimistic-locking
http-status
Intermediate
6 steps