Singleton

The Singleton pattern is an OOP design pattern that ensures a class has at most one instance and provides a global access point to that instance. In both 3D applications (for example scene or resource managers, renderers or physics worlds) and web projects (for example database connections or authentication services), a singleton is used to centralize shared resources and coordination. Implementations use static members, modules/closures or framework-specific mechanisms (such as Unity's static instance or ES modules in frontend and Node.js); be aware of downsides like hidden dependencies, harder testing, lifecycle issues and concurrency concerns on servers or across workers.

In a 3D project you might have a Renderer or AssetLoader singleton: a single central object creates and manages the GPU context, texture caches and loading queues so all 3D objects reuse the same renderer and resources. In Unity you often see a GameManager with a static Instance field that holds global game state and settings; in native engines this might be the PhysicsWorld or SceneManager. On the web you can apply the same pattern for a database or API client in Node.js, or for an AuthService in a frontend app (e.g. a single instance that manages tokens). A practical web implementation often leverages ES modules as singletons, while 3D engines may use static fields or engine-level singletons — remember to handle cleanup on hot-reload and in tests to avoid leaks.