Singleton Design Pattern — 3 Minute Series

One instance globally.

Photo by Chetan Hireholi on Unsplash

_00 / Concept

In an application, the Singleton design pattern can ensure the app has only one instance globally.

_01 / Key Roles

class LogService {
  private static instance = null; 
  private constructor() {}
  static init() {
    if (this.instance === null) {
      this.instance = new LogService();
    }
    return this.instance
  }
  ...
}
const logger = LogService.init();
logger...

_02 / Trade-offs

🟢 Eliminated unnecessary instantiation.
🔴 Introduce a global variable and states which is bad for testing.
🔴 Singleton solves less than it causes, so make sure you need it.