Gang of Four patterns simplified
Ensure only one instance exists. Config, DB connection
Create objects without specifying exact class. Button factory
Construct complex objects step by step. Query builder
Convert one interface to another. API adapter
Add behavior dynamically. Express middleware
Simplified interface to complex subsystem. Service layer
One-to-many dependency. Event emitter, pub/sub
Interchangeable algorithms. Sort strategies
Encapsulate requests as objects. Undo/redo