bird.js

function createBird() {
    let distance = 0
    let self =  {
        fly(A = 1) {
            distance += A
            return self
        },

        getDistance() {
            return distance
        },

        compareWith(bird) {
            return bird.getDistance() > distance 
                ? 'Another bird win' 
                : 'I win'
        }
    }

    return self
}

const bird1 = createBird();
const bird2 = createBird();
const bird3 = createBird();

bird1.fly()
bird1.fly()
assert(bird1.getDistance()).toBe(2)

bird2.fly().fly().fly()
assert(bird2.getDistance()).toBe(3)

bird2.fly(3)
assert(bird2.getDistance()).toBe(6)

bird1.fly(2).fly().fly(1)
assert(bird1.getDistance()).toBe(6)

bird1.fly(3)
assert(bird1.getDistance()).toBe(9)

bird3.fly(2)
assert(bird2.compareWith(bird3)).toBe('I win');
assert(bird1.compareWith(bird3)).toBe('I win');
assert(bird3.compareWith(bird1)).toBe('Another bird win');

bird3.fly(50)
assert(bird1.compareWith(bird3)).toBe('Another bird win');