composition in js

equivalent_composition_version.js

function walker({name}) {
    return {
        walk: () => console.log(name + ' can walk'),
    }
}
function attacker({name}) {
    return {
        attack: () => console.log(name + ' can attack'),
}
}
function swimmer({name}) {
    return {
        swim: () => console.log(name + ' can swim'),
}
}
function flyer({name}) {
    return {
        fly: () => console.log(name + ' can fly'),
}
}

function monster(name) {
    return {
        ...walker({name}),
        ...attacker({name}),
    }
}

function flyingMonster(name) {
    return {
        ...flyer({name}),
        ...attacker({name}),
    }
}
function swimmingMonster(name) {
    return {
        ...swimmer({name}),
        ...attacker({name}),
    }
}

const daynasor = monster('daynasor');
daynasor.walk();
daynasor.attack();

const qrsh = swimmingMonster('qrsh');
qrsh.swim();
qrsh.attack();

const saqar = flyingMonster('saqar');
saqar.fly();
saqar.attack();

old_way_using_inheritance.js

class Monster {
    constructor(name) {
        this.name = name;
    }
    attack() {
        console.log(this.name + ' can attack');
    }
    walk() {
        console.log(this.name + ' can walk');
    }
}

class FlyingMonster extends Monster {
    fly() {
        console.log(this.name + ' can fly');
    }
}

class SwimmingMonster extends Monster {
    swim() {
        console.log(this.name + ' can swim');
    }
}

const daynasor = new Monster('daynasor');
const qrsh = new SwimmingMonster('qrsh');
const saqar = new FlyingMonster('saqar');

daynasor.attack();
daynasor.walk();

qrsh.walk(); // this is not right
qrsh.attack();
qrsh.swim();

saqar.walk();
saqar.attack();
saqar.fly();