Visitor
Represents an operation to be performed on elements of an object structure. Lets you define a new operation without changing the classes of the elements.
Visitor: Operations over Object Structures
Adding operations to objects without changing their classes — a visitor walks the structure.
Visitor in Production: Compilers and Analyzers
AST visitors in compilers, linters, and formatters — real production visitors.
Advanced Visitor: Extensible and Generic Visitors
Type-safe visitors, generics, and avoiding the expression problem.
Visitor: Review & Mastery Quiz
Scenario questions on dispatch, operations, and the expression problem.
Free Books & Guides
Refactoring.Guru — Visitor
The definitive modern guide to the Visitor pattern. Clear explanations, UML diagrams, real-world analogies, and code examples in multiple languages.
SourceMaking — Visitor
A comprehensive companion guide covering the Visitor pattern with detailed rules of thumb, criticisms, and robust code snippets.
GoF Design Patterns — Visitor
The original Gang of Four book describing the pattern. Available in the "Design Patterns: Elements of Reusable Object-Oriented Software" on Wikipedia.
Official Documentation
Video Courses
freeCodeCamp — Design Patterns Course
A comprehensive multi-hour video course covering all major design patterns with implementations in JavaScript and TypeScript.
Design Patterns in Modern JavaScript Playlist
YouTube playlist covering creational, structural, and behavioral patterns with clear code walkthroughs.
Web Dev Simplified — Visitor
Clear, concise video tutorials covering design patterns with practical examples.
Practice & Examples
Awesome Low-Level Design (GitHub)
A curated collection of free LLD resources, pattern implementations, and interview problems across multiple languages.
Design Patterns Implementation (GitHub)
The most popular open-source collection of design pattern implementations with detailed explanations.
Refactoring.Guru Examples in Visitor
Code examples of the Visitor pattern in TypeScript, Python, Java, and more.