How to define Singleton in TypeScript

Since TS 2.0, we have the ability to define visibility modifiers on constructors, so now we can do singletons in TypeScript just like we are used to from other languages.

Example given:

class MyClass
{
    private static _instance: MyClass;

    private constructor()
    {
        //...
    }

    public static get Instance()
    {
        // Do you need arguments? Make it a regular static method instead.
        return this._instance || (this._instance = new this());
    }
}

const myClassInstance = MyClass.Instance;

---

Thank you @Drenai for pointing out that if you write code using the raw compiled javascript you will not have protection against multiple instantiation, as the constraints of TS disappears and the constructor won't be hidden.

Singleton classes in TypeScript are generally an anti-pattern. You can simply use namespaces instead.

Useless singleton pattern

class Singleton {
    /* ... lots of singleton logic ... */
    public someMethod() { ... }
}

// Using
var x = Singleton.getInstance();
x.someMethod();

Namespace equivalent

export namespace Singleton {
    export function someMethod() { ... }
}
// Usage
import { SingletonInstance } from "path/to/Singleton";

SingletonInstance.someMethod();
var x = SingletonInstance; // If you need to alias it for some reason

The best way I have found is:

class SingletonClass {

    private static _instance:SingletonClass = new SingletonClass();

    private _score:number = 0;

    constructor() {
        if(SingletonClass._instance){
            throw new Error("Error: Instantiation failed: Use SingletonClass.getInstance() instead of new.");
        }
        SingletonClass._instance = this;
    }

    public static getInstance():SingletonClass
    {
        return SingletonClass._instance;
    }

    public setScore(value:number):void
    {
        this._score = value;
    }

    public getScore():number
    {
        return this._score;
    }

    public addPoints(value:number):void
    {
        this._score += value;
    }

    public removePoints(value:number):void
    {
        this._score -= value;
    }

}

Here is how you use it:

var scoreManager = SingletonClass.getInstance();
scoreManager.setScore(10);
scoreManager.addPoints(1);
scoreManager.removePoints(2);
console.log( scoreManager.getScore() );

https://codebelt.github.io/blog/typescript/typescript-singleton-pattern/