How to implement Singleton in Node.js

How to implement Singleton in Node.js

https://grokonez.com/node-js/how-to-implement-singleton-in-node-js-example

Singleton is object that can have only a single, unique instance, with a single point of access. Node.js module system provides simple way to implement Singleton using module.exports. Module will be cached when it is accessed using require() statement. So our module is merely a cached instance although it behaves like a Singleton.

In this tutorial, we're gonna look at ways to implement this kind of Singleton in Node.js:

• Singleton Object
• Singleton Class

Node.js Singleton Object example

We will create a Bank object, it has 3 methods:

• deposit() increases cash.
• withdraw() decreases cash.
• total() returns cash.

Bank.js

let cash = 0;

const Bank = {
    deposit(amount) {
        cash += amount;
        return cash;
    },
    withdraw(amount) {
        if (amount <= cash) {
            cash -= amount;
            return true;
        } else {
            return false;
        }
    },
    total() {
        return cash;
    }
}

module.exports = Bank;

Bank object behaves like a Singleton because we will use module.exports and require() statement (not use new keyword).

app.js

const fund = require('./Bank');
const atm1 = require('./Bank');
const atm2 = require('./Bank');

fund.deposit(10000)

atm1.deposit(20)
atm2.withdraw(120)

console.log(`total-atm1: ${atm1.total()}`)
console.log(`total-atm2: ${atm2.total()}`)

fund.deposit(2000)
console.log(`total-fund: ${fund.total()}`)

As you can see, we create 3 Banks (fund, atm1, atm2), every Bank object can deposit or withdraw money. But all of the action work with only one the cash insides Bank.

Here is the result (run with node app.js command):

total-atm1: 9900
total-atm2: 9900
total-fund after funding 2000: 11900

More at: https://grokonez.com/node-js/how-to-implement-singleton-in-node-js-example