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Written for developers. Structured for AI citation.

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1.4k terms across 32 categories — definitions, examples, common mistakes and fixes. Authored under one editorial standard. Cross-linked, searchable, and openly crawled by AI agents.

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Undefined Array Key / Offset Errors 3 Database Deadlocks 3 Exception Handling (try/catch/finally) 3 Accessible Forms 3 Observer Pattern 3 Path Traversal 3 Amortized Analysis 3 Destructuring & Spread (JS) 2

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Diagram: Covariance & Contravariance

Covariance & Contravariance 4.7

Variance describes how subtype relationships on a type's components affect subtype relationships on the whole type — covariant types follow the direction, contravariant types reverse it.

4w ago typescript advanced

Diagram: Discriminated Unions

Discriminated Unions 2.0

A union of types that each carry a shared literal field (the discriminant) allowing TypeScript to narrow exhaustively — the canonical way to model mutually exclusive states.

4w ago typescript intermediate

Diagram: Module Augmentation & Declaration Merging

Module Augmentation & Declaration Merging 2.0

Module augmentation lets you extend third-party or global type definitions without modifying their source — adding properties to existing interfaces, modules, or the global scope.

4w ago typescript advanced

Diagram: Recursive Types

Recursive Types 3.7

Types that reference themselves to describe arbitrarily nested structures — trees, nested menus, JSON, linked lists — without requiring any escape hatch.

4w ago typescript advanced

Diagram: Type Guards & Narrowing

Type Guards & Narrowing 2.0

Type guards are expressions that narrow a union type to a more specific type at runtime — telling TypeScript exactly which branch of a union you're in.

4w ago typescript intermediate

async / await in JavaScript ES2017

async functions always return a Promise; await pauses execution inside an async function until a Promise settles — giving asynchronous code the readability of synchronous code without blocking the event loop.

4w ago javascript intermediate

Brute-Force Protection

Defences against automated credential-guessing attacks — rate limiting login attempts, account lockout, CAPTCHA, and multi-factor authentication to make guessing passwords computationally infeasible.

CWE-307 OWASP A7:2021

4w ago security intermediate

ES Modules (ESM) ES2015

The official JavaScript module system — import and export statements enable static dependency graphs, tree-shaking, and native browser module loading without a bundler.

4w ago javascript intermediate

Fetch API ES2015

The browser-native Promise-based API for making HTTP requests — replacing XMLHttpRequest with a cleaner interface supporting streaming, CORS, and request/response objects.

4w ago javascript beginner

HTTP Cookies in PHP PHP 7.3+

Cookies are small key-value pairs sent by the server via Set-Cookie and echoed back by the browser on every request — PHP sets them with setcookie() before any output, with Secure, HttpOnly, and SameSite flags controlling safety.

4w ago php beginner

Insecure Deserialization

Deserializing attacker-controlled data can trigger arbitrary object construction and method calls — PHP's unserialize() with untrusted input enables remote code execution via gadget chains in the loaded class graph.

CWE-502 OWASP A8:2021

4w ago security advanced

Memory Management in JavaScript

JavaScript uses automatic garbage collection — the engine reclaims memory when objects are no longer reachable. Memory leaks occur when references are unintentionally retained, preventing collection.

4w ago javascript intermediate

An authorisation framework that lets users grant third-party applications limited access to their resources without sharing passwords — using short-lived access tokens issued via defined flows for different client types.

CWE-287 OWASP A7:2021

4w ago security intermediate

Side-channel attacks that infer secret values by measuring how long an operation takes — a string comparison that short-circuits on the first mismatch leaks information about the secret one character at a time.

4w ago security advanced

Canonical URL (rel=canonical)

A <link rel='canonical'> tag that tells search engines which URL is the authoritative version of a page — preventing duplicate content from splitting ranking signals across multiple URLs.

1mo ago frontend intermediate

Core Web Vitals

Google's three field-measured performance metrics — LCP (loading), INP (interactivity), CLS (visual stability) — used as direct search ranking signals since 2021.

1mo ago performance intermediate

Cumulative Layout Shift (CLS)

A Core Web Vital that measures unexpected visual movement of page elements during load — caused by images without dimensions, late-injected content, and font swaps. Target: under 0.1.

1mo ago performance intermediate

Dependency & Supply Chain Security

Protecting applications from malicious or vulnerable third-party packages — covering transitive dependencies, lock files, SRI hashes, CVE scanning, and supply chain attack vectors.

CWE-1357 OWASP A6:2021

1mo ago security intermediate

HTML lang Attribute

The lang attribute on <html> declares the page's primary language — required for screen readers to select the correct voice profile and pronunciation rules, and for WCAG 2.1 compliance.

1mo ago accessibility beginner

Tags in <head> that provide page metadata — title, description, viewport, Open Graph — for browsers, search engines, and social platforms.

1mo ago frontend beginner

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