Intermediate code explainers

python

from functools import lru_cache
 
 
class SpellingSuggester:

A spelling suggester with edit distance

edit-distance dynamic-programming memoization

Intermediate 9 steps

javascript

const FRONTMATTER_RE = /^---\r?\n([\s\S]*?)\r?\n---\r?\n?/;
 
function coerce(value) {
  const trimmed = value.trim();

Parsing YAML-style frontmatter in JavaScript

parsing regular-expressions type-coercion

Intermediate 9 steps

typescript

import { Exclude, Expose, Transform, Type } from 'class-transformer';
 
export class AddressEntity {
  street: string;

Shaping API responses with class-transformer in NestJS

serialization decorators dto

Intermediate 10 steps

javascript

const IDLE_TIMEOUT = 15 * 60 * 1000;
const WARNING_BEFORE = 60 * 1000;
const ACTIVITY_EVENTS = ['mousemove', 'keydown', 'scroll', 'touchstart', 'click'];

How an idle-session monitor logs you out

timers throttling broadcastchannel

Intermediate 8 steps

javascript

import { ImageResponse } from 'next/og'
 
export function manifest() {
  return {

Generating a PWA manifest and icon in Next.js

pwa metadata og-image

Intermediate 9 steps

rust

use axum::{
    extract::{Path, State},
    http::StatusCode,
    response::IntoResponse,

Building a GitHub proxy handler in Axum

shared-state http-client error-mapping

Intermediate 9 steps

typescript

import { Injectable, inject } from '@angular/core';
import { MatDialog } from '@angular/material/dialog';
import { Observable, of } from 'rxjs';
import { switchMap } from 'rxjs/operators';

A reusable confirmation dialog service in Angular

dependency-injection observables dialog

Intermediate 6 steps

python

from django.db import transaction
from django.forms import inlineformset_factory
from django.shortcuts import get_object_or_404, redirect, render

Editing an order with inline formsets in Django

formsets transactions crud

Intermediate 9 steps

javascript

function isValidCardNumber(input) {
  const digits = String(input).replace(/[\s-]/g, '');
 
  if (!/^\d{13,19}$/.test(digits)) {

Validating card numbers with Luhn

checksum validation luhn-algorithm

Intermediate 7 steps

python

from flask import Blueprint, render_template, jsonify, request, abort
 
from .models import Article

Content negotiation in a Flask Blueprint

content-negotiation http-headers routing

Intermediate 7 steps

go

package handlers
 
import (
	"net/http"

Sparse fieldsets in a Gin handler

sparse-fieldsets query-parsing json-serialization

Intermediate 9 steps

javascript

import { useEffect, useState } from 'react';
 
export function useJobStatus(jobId, { interval = 3000 } = {}) {
  const [status, setStatus] = useState('pending');

Polling a job status with a React hook

custom-hooks polling cleanup

Intermediate 8 steps

typescript

import { Directive, ElementRef, HostBinding, HostListener, Input, inject, signal } from '@angular/core';
 
@Directive({
  selector: '[appCopyToClipboard]',

A copy-to-clipboard directive in Angular

directives host bindings clipboard api

Intermediate 9 steps

rust

use std::collections::BTreeSet;
use std::fs::File;
use std::io::{self, BufRead, BufReader, BufWriter, Write};
use std::path::Path;

Deduplicating and sorting words in Rust

file-io btreeset string-processing

Intermediate 6 steps

ruby

module Api
  module Reports
    class DailyOrderTotalsController < Api::BaseController
      def index

Building a daily order totals report in Rails

sql aggregation json api query building

Intermediate 7 steps

python

import os
import shutil
import tempfile
from contextlib import contextmanager

Transactional file operations in Python

transactions rollback closures

Intermediate 8 steps

php

<?php
 
namespace App\Storage;

A race-free file counter in PHP

file-locking concurrency atomicity

Intermediate 7 steps

go

package sse
 
import (
	"encoding/json"

Server-Sent Events streaming in Go

server-sent-events channels http-streaming

Intermediate 8 steps