Singleton Design Pattern
- Singletons are objects that can only have a single instance, with a single point of access
- The module system in nodejs offers a rudimentary implementation of a singleton
- In modules, single instance of class is created and cached
Example
// CashRegister.js
let cash = 0
const CashRegister = {
credit(amount) {
cash = cash + amount
return cash
},
debit(amount) {
if (amount <= cash) {
cash = cash - amount
return true
} else {
return false
}
},
total() {
return cash
},
}
module.exports = CashRegister// App.js
const cashRegister = require('./CashRegister')
const cashRegister2 = require('./CashRegister')
cashRegister.credit(10)
cashRegister2.credit(20)
cashRegister.debit(5)
console.log(cashRegister.total()) // answer is 25 as both object are using same instance