an example of how to implement an immutable counter

immutable_counter.js

(() => { 
	class Counter { 
		constructor(start_value) {
			this.plus = this.plus(start_value)
		}  
		
	plusFn(num, _num) {
		var res = num + _num
			this.plus = (_num) => {
				return this.plusFn(res, _num)
			}
			return res
		}

		plus(num) {
			return (_num) => { 
				return this.plusFn(num, _num)
			}
		} 

	}  

	var myCounter = new Counter(1)

	console.log(myCounter.plus(1)) // 2
	console.log(myCounter.plus(1)) // 3 
	console.log(myCounter.plus(3)) // 6
})()