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Singleton

Ensures a class has only one instance and provides a global point of access to it.

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errorThe Challenge

Some resources—database connections, configuration managers, logging services—should exist as a single shared instance. Creating multiple instances wastes memory, causes inconsistent state, and can lead to race conditions in concurrent environments.

check_circleThe Solution

Make the constructor private and provide a static method that always returns the same instance. On first call, the instance is created; on subsequent calls, the existing instance is returned. Thread-safe variants use double-checked locking or language-level guarantees.

Architecture Overview

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Implementation

class Singleton {
  private static instance: Singleton;

  private constructor() {
    // Private constructor prevents direct instantiation
  }

  static getInstance(): Singleton {
    if (!Singleton.instance) {
      Singleton.instance = new Singleton();
    }
    return Singleton.instance;
  }

  // Business methods
  doSomething(): void {
    console.log("Singleton method called");
  }
}

// Usage
const a = Singleton.getInstance();
const b = Singleton.getInstance();
console.log(a === b); // true

Compiled with TypeScript 5.6

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Real-World Analogy

“Think of a country’s president. There can only be one at any time. When anyone needs to communicate with the president, they don’t create a new one—they access the existing one through the official channel (the static method).”