Code Explainers
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javascript
const fs = require('fs'); const path = require('path'); router.get('/downloads/:name', (req, res, next) => {
Streaming file downloads in Express
streaming
backpressure
file-download
Advanced
9 steps
ruby
module Retryable class RetriesExhausted < StandardError; end RETRYABLE_ERRORS = [
Exponential backoff retries in Ruby
retry-logic
exponential-backoff
error-handling
Intermediate
7 steps
typescript
import { IsEmail, IsEnum, IsInt, IsOptional, IsString, Length, Max, Min } from 'class-validator'; import { Type } from 'class-transformer'; import { Body, Controller, Post } from '@nestjs/common';
How DTO validation works in NestJS
validation
data-transfer-objects
decorators
Intermediate
8 steps
go
package worker import ( "fmt"
A graceful worker pool in Go
concurrency
goroutines
channels
Intermediate
7 steps
java
@Repository public interface OrderRepository extends JpaRepository<Order, Long> { @QueryHints(@QueryHint(name = HINT_FETCH_SIZE, value = "1000"))
Streaming large result sets in Spring Data JPA
streaming
jpa
memory-management
Advanced
6 steps
javascript
async function pollJobUntilComplete(jobId, { interval = 2000, timeout = 60000, signal } = {}) { const deadline = Date.now() + timeout; while (true) {
Polling a job until it finishes in JavaScript
polling
async-await
abortsignal
Intermediate
6 steps
ruby
class Throttle def initialize(interval) @interval = interval @mutex = Mutex.new
A thread-safe throttle in Ruby
concurrency
rate-limiting
mutex
Intermediate
7 steps
typescript
type CheckoutState = "cart" | "shipping" | "payment" | "review" | "confirmed"; type CheckoutEvent = | { type: "PROCEED" }
A typed checkout state machine in TypeScript
state-machine
union-types
type-safety
Intermediate
7 steps
go
package handlers import ( "net/http"
Rendering HTML pages with Gin handlers
http-handlers
templating
error-handling
Beginner
8 steps
rust
use axum::{ body::Body, extract::Path, http::{header, StatusCode},
Streaming file downloads in Axum
streaming
file-serving
path-traversal
Intermediate
8 steps
java
import java.util.ArrayList; import java.util.Comparator; import java.util.HashSet; import java.util.List;
Three ways to deduplicate a list by key in Java
streams
deduplication
collectors
Intermediate
6 steps
php
<?php function verifyJwt(string $token, string $secret): array {
Verifying an HS256 JWT in PHP
jwt
hmac
authentication
Intermediate
9 steps
python
from fastapi import FastAPI, Request, status from fastapi.responses import JSONResponse app = FastAPI()
Custom exception handlers in FastAPI
exception handling
error responses
separation of concerns
Intermediate
7 steps
ruby
class Article < ApplicationRecord before_validation :generate_slug, on: :create validates :slug, presence: true, uniqueness: true,
How URL slugs work in Rails
callbacks
validations
slugs
Intermediate
7 steps
ruby
class CheckoutService Result = Struct.new(:success?, :order, :error, keyword_init: true) def self.call(...)
How a Rails checkout service object works
service object
transactions
result object
Intermediate
9 steps
ruby
class User < ApplicationRecord has_one_attached :avatar validate :acceptable_avatar
Validating and serving avatars with Active Storage in Rails
active storage
file uploads
validation
Intermediate
9 steps
ruby
class Article < ApplicationRecord belongs_to :author default_scope { where(deleted_at: nil) }
How scopes compose in Rails
scopes
query-composition
activerecord
Intermediate
9 steps
ruby
class Employee < ApplicationRecord validates :name, presence: true validates :salary, numericality: { greater_than: 0 }
How STI models share behavior in Rails
single-table-inheritance
inheritance
method-overriding
Intermediate
8 steps