Code Explainers

Code explainers tagged #closures

rust 
pub struct ScopeGuard<F: FnMut()> {
    rollback: F,
    active: bool,
}

A RAII rollback guard in Rust

raii error-handling closures
Advanced 8 steps
javascript 
function makeTableSorter(rows) {
  const state = { key: null, dir: 1 };
 
  const compareBy = (key) => (a, b) => {

Building a stateful table sorter in JavaScript

closures stable-sort comparators
Intermediate 7 steps
javascript 
function createAutocomplete(input, resultsList, { minChars = 2, delay = 300 } = {}) {
  let timer = null;
  let controller = null;
 

Building a debounced autocomplete widget

debouncing abortcontroller closures
Intermediate 9 steps
typescript 
type Curried<A extends any[], R> = A extends [infer First, ...infer Rest]
  ? (arg: First) => Rest extends [] ? R : Curried<Rest, R>
  : R;
 

Type-safe currying in TypeScript

currying conditional-types recursion
Advanced 8 steps
php 
<?php
 
namespace App\Http;
 

Building an onion middleware pipeline in PHP

middleware closures array-reduce
Advanced 9 steps
typescript 
type EventMap = Record<string, unknown>;
 
type Handler<T> = (payload: T) => void;
 

A type-safe event bus in TypeScript

generics event-emitter type-safety
Advanced 7 steps
go 
package middleware
 
import (
	"crypto/subtle"

Building an API-key middleware in Gin

middleware authentication dependency-injection
Intermediate 5 steps
javascript 
class EventEmitter {
  constructor() {
    this.listeners = new Map();
  }

Building an EventEmitter in JavaScript

pub-sub closures map
Intermediate 7 steps
go 
package web
 
import (
	"embed"

Serving embedded static assets in Go

embed static-assets http-handler
Intermediate 8 steps
javascript 
function createCountdownTimer(durationSeconds, { onTick, onComplete } = {}) {
  let remaining = durationSeconds;
  let intervalId = null;
 

Building a countdown timer with closures

closures factory-function timers
Intermediate 9 steps
javascript 
const crypto = require('crypto');
 
function securityHeaders(options = {}) {
  const {

A configurable security-headers middleware in Express

middleware http-headers content-security-policy
Intermediate 7 steps
javascript 
const cache = new Map();
const inflight = new Map();
 
async function fetchResults(query) {

Building a typeahead with an LRU cache

caching lru-eviction request-deduplication
Intermediate 9 steps
javascript 
export function createSearchClient(baseUrl) {
  let inFlight = null;
 
  async function search(query, { signal } = {}) {

Cancelling stale requests in a search client

closures abortcontroller async
Intermediate 8 steps
go 
package middleware
 
import (
	"time"

Building a request logger middleware in Gin

middleware structured-logging closures
Intermediate 6 steps
go 
package auth
 
import (
	"net/http"

Building a JWT auth middleware in Gin

middleware jwt authentication
Intermediate 7 steps
go 
package server
 
import (
	"context"

Composing HTTP middleware in Go

middleware http-handlers closures
Intermediate 8 steps
ruby 
def build_tree(rows, root_id: nil)
  children_by_parent = Hash.new { |hash, key| hash[key] = [] }
 
  rows.each do |row|

Building a tree from flat rows in Ruby

recursion hash-grouping tree-structure
Intermediate 5 steps
php 
<?php
 
namespace App\Http\Controllers;
 

Building a filtered product index in Laravel

query-builder validation conditional-queries
Intermediate 9 steps