Code Explainers

Code explainers tagged #closures

javascript 
function evaluate(expression) {
  const tokens = tokenize(expression);
  let pos = 0;
 

Building a recursive descent calculator

parsing recursion operator-precedence
Intermediate 8 steps
python 
from typing import Any, Sequence, Mapping
 
 
def render_markdown_table(

Rendering an aligned Markdown table in Python

string formatting data transformation closures
Intermediate 8 steps
go 
package config
 
import (
	"os"

Layered config resolution in Go

configuration closures higher-order-functions
Intermediate 8 steps
php 
<?php
 
namespace App\Http\Controllers;
 

Conditional query building in Laravel

query-builder conditional-logic closures
Intermediate 7 steps
go 
func HandleWebhook(store WebhookStore, dispatcher *EventDispatcher) gin.HandlerFunc {
	return func(c *gin.Context) {
		body, err := c.GetRawData()
		if err != nil {

Building a resilient webhook handler in Gin

webhooks dependency-injection signature-verification
Intermediate 9 steps
go 
package middleware
 
import (
	"crypto/subtle"

Timing-safe API key auth in Gin

middleware authentication constant-time-compare
Intermediate 8 steps
python 
from fastapi import APIRouter, Depends, HTTPException, status
 
from app.config import settings
from app.dependencies import get_current_user

Gating a FastAPI route behind a feature flag

feature-flags dependency-injection authorization
Intermediate 7 steps
javascript 
class ShortcutManager {
  constructor(target = window) {
    this.target = target;
    this.bindings = new Map();

Building a keyboard shortcut manager in JavaScript

event-handling normalization map
Intermediate 9 steps
python 
from functools import wraps
from flask import request, jsonify
 
 

A parameterized query-param decorator in Flask

decorators validation type-casting
Intermediate 8 steps
javascript 
import { useEffect, useRef } from 'react';
 
export function useOnClickOutside(handler) {
  const ref = useRef(null);

A click-outside hook in React

custom-hooks refs event-listeners
Intermediate 7 steps
typescript 
type QueryValue = string | number | boolean | null | undefined;
type QueryInput = QueryValue | QueryValue[] | { [key: string]: QueryInput };
 
function buildQueryString(params: Record<string, QueryInput>): string {

Building nested query strings recursively

recursion url-encoding serialization
Intermediate 8 steps
go 
package middleware
 
import (
	"fmt"

How a panic-recovery middleware works in Gin

middleware panic-recovery error-reporting
Intermediate 8 steps
rust 
use std::time::Duration;
 
#[derive(Debug, Clone, Copy)]
pub struct LatencyStats {

Computing latency percentiles in Rust

percentiles interpolation closures
Intermediate 6 steps
typescript 
type Countdown = {
  days: number;
  hours: number;
  minutes: number;

Building a self-stopping countdown timer

date-math closures timers
Intermediate 9 steps
rust 
use once_cell::sync::Lazy;
use regex::Regex;
 
static CREDIT_CARD: Lazy<Regex> = Lazy::new(|| {

Redacting sensitive data from logs in Rust

regex lazy-initialization checksum-validation
Intermediate 9 steps
go 
package middleware
 
import (
	"net/http"

A content-type guard middleware in Gin

middleware closures http
Intermediate 7 steps
php 
<?php
 
namespace App\Providers;
 

Defining authorization gates in Laravel

authorization gates service-provider
Intermediate 6 steps
go 
package middleware
 
import (
	"net/http"

Role-based access control middleware in Gin

middleware authorization closures
Intermediate 7 steps