Module 22: Design Patterns

Overview

This module covers essential software design patterns applied to JavaScript. Design patterns are reusable solutions to common problems in software design, helping you write more maintainable, flexible, and scalable code.

Learning Objectives

By the end of this module, you will be able to:

•Understand and implement creational patterns
•Apply structural patterns for code organization
•Use behavioral patterns for object communication
•Recognize when to apply specific patterns
•Combine patterns effectively

Prerequisites

•Module 10: Objects (object manipulation)
•Module 11: Classes (OOP fundamentals)
•Module 5: Functions (higher-order functions, closures)

Sections

22.1 Creational Patterns

•Factory Pattern
•Abstract Factory
•Builder Pattern
•Singleton Pattern
•Prototype Pattern

22.2 Structural Patterns

•Adapter Pattern
•Decorator Pattern
•Facade Pattern
•Proxy Pattern
•Module Pattern

22.3 Behavioral Patterns

•Observer Pattern
•Strategy Pattern
•Command Pattern
•Iterator Pattern
•State Pattern

22.4 Functional Patterns

•Composition
•Currying and Partial Application
•Memoization
•Middleware Pattern
•Pipeline Pattern

22.5 Architectural Patterns

•MVC/MVP/MVVM
•Flux/Redux Pattern
•Event Sourcing
•Repository Pattern
•Dependency Injection

Pattern Categories Overview

┌────────────────────────────────────────────────────────────────────────────┐
│                       Design Pattern Categories                            │
├────────────────────────────────────────────────────────────────────────────┤
│                                                                            │
│   ┌───────────────┐  ┌───────────────┐  ┌───────────────┐                  │
│   │  Creational   │  │  Structural   │  │  Behavioral   │                  │
│   │  Patterns     │  │  Patterns     │  │  Patterns     │                  │
│   └───────┬───────┘  └───────┬───────┘  └───────┬───────┘                  │
│           │                  │                  │                          │
│   • Factory           • Adapter         • Observer                         │
│   • Singleton         • Decorator       • Strategy                         │
│   • Builder           • Facade          • Command                          │
│   • Prototype         • Proxy           • State                            │
│                       • Module          • Iterator                         │
│                                                                            │
│   "How objects        "How objects      "How objects                       │
│    are created"        are composed"     communicate"                      │
│                                                                            │
└────────────────────────────────────────────────────────────────────────────┘

Quick Pattern Reference

Pattern	Purpose	JavaScript Example
Factory	Create objects without `new`	`createUser(data)`
Singleton	Single instance globally	`export default instance`
Observer	Pub/sub event system	`EventEmitter`
Decorator	Add behavior dynamically	`@decorator` or HOC
Strategy	Interchangeable algorithms	`validator.setStrategy()`
Facade	Simplified interface	jQuery wrapping DOM
Proxy	Control access to object	ES6 `Proxy` object
Module	Encapsulation with public API	IIFE or ES Modules

File Structure

Module-22-Design-Patterns/
├── README.md
├── 22.1-Design-Patterns-Overview/
│   ├── README.md
│   ├── examples.js
│   └── exercises.js
├── 22.2-Structural-Patterns/
│   ├── README.md
│   ├── examples.js
│   └── exercises.js
├── 22.3-Behavioral-Patterns/
│   ├── README.md
│   ├── examples.js
│   └── exercises.js
├── 22.4-Functional-Patterns/
│   ├── README.md
│   ├── examples.js
│   └── exercises.js
└── 22.5-Architectural-Patterns/
    ├── README.md
    ├── examples.js
    └── exercises.js

Best Practices

•Don't over-engineer - Use patterns when they solve real problems
•Favor composition - Over deep inheritance hierarchies
•Keep it simple - The simplest solution is often best
•Document patterns used - Help other developers understand
•Combine patterns wisely - Patterns often work together

Next Steps

After completing this module, proceed to:

•Module 23: Performance Optimization
•Module 24: JavaScript Engine Internals