Simple calculator with function chaining

index.js

const plus = (a, b) => a + b;
const minus = (a, b) => a - b;
const multiply = (a, b) => a * b;
const divide = (a, b) => a / b;

const Calc = (a) => ({
	plus: (...b) => Calc(b.reduce(plus, a)),
	minus: (...b) => Calc(b.reduce(minus, a)),
	multiply: (...b) => Calc(b.reduce(multiply, a)),
	divide: (...b) => Calc(b.reduce(divide, a)),
	value: () => a
});
module.exports = Calc

index.spec.js

const Calc = require('./index');

let calc;
describe('calculator', () => {
	beforeEach(() => {
		calc = Calc(10);
	});
	it('plus', () => {
		expect(calc.plus(3).value()).toBe(13);
	});
	it('minus', () => {
		expect(calc.minus(2).value()).toBe(8);
	});
	it('multiply once', () => {
		expect(calc.multiply(2).value()).toBe(20);
	});
	it('multiply several', () => {
		expect(calc.multiply(2, 5).value()).toBe(100);
	});
	it('divide', () => {
		expect(calc.divide(2).value()).toBe(5);
	});
	it('divide several', () => {
		expect(calc.divide(2, 2).value()).toBe(2.5);
	});
	it('combination', () => {
		expect(calc.plus(2).multiply(2, 4).divide(3).value()).toBe(32);
	});
});