singleton in javascript

class Singleton
{
    constructor()
    {
        if (!Singleton.instance)
        {
            Singleton.instance = this;
        }
        return Singleton.instance;
    }

    getInstance()
    {
        return this.instance;
    }
}

test

const testA = new Singleton();
const testB = new Singleton();

console.log(testA === testB); // true

singleton example (db connection)

const URL = "db_url";
const createConnection = url => ({"url" : url});
class DB
{
    constructor(url)
    {
        if (!DB.instance)
        {
            DB.instance = createConnection(url);
        }
        return DB.instance;
    }

    connect()
    {
        return this.instance;
    }
}