es6-with-traits

A traits mechanism for ES6 with support for "methodical interface checking"

Usage

let {Trait, withTraits} = require('es6-with-traits');

class Animal {}
let Flying = Trait(function(parentClass) {
    return class Flying extends parentClass {
        constructor(...args) {
            super(...args);
            this.wings = ["left wing", "right wing"];
        }
        fly() {
            console.log("flap flap with the " + this.wings.join(" and "));
        }
    };
});
let Walking = Trait(function(parentClass) {
    return class Walking extends parentClass {
        constructor(...args) {
            super(...args);
            this.legs = this.legs || []; // there must be legs, by default we don't know how many

            // Also to be researched (as an alternative to the above):
            // Legged.check(this);
        }
        walk() {
            console.log("walking on legs " + this.legs.join(" and "));
        }
    };
});
let Biped = Trait(function(parentClass) {
    return class Biped extends parentClass {
        constructor(...args) {
            super(...args);
            this.legs = ["left leg", "right leg"];
        }
    };
});
let Quadruped = Trait(function(parentClass) {
    return class Quadruped extends parentClass {
        constructor(...args) {
            super(...args);
            this.legs = ["front left leg", "front right leg", "rear left leg", "rear right leg"];
        }
    };
});

class Dog extends withTraits(Animal, Quadruped, Walking) {}
class Bird extends withTraits(Animal, Biped, Walking, Flying) {}
let dog = new Dog();
console.log("dog.walk():");
dog.walk();

let bird = new Bird();
console.log("bird.walk():");
bird.walk();
console.log("bird.fly():");
bird.fly();

console.log("Does a dog walk?", Walking.check(dog)); // => true
console.log("Does a dog fly?", Flying.check(dog)); // => false

var duck = {
    legs: [],
    walk: function() {},
    fly: function() {}
};

console.log("Is a duck a bird?", Bird.check(duck)); // => true

// Of course, not everything is perfect (yet):
console.log("Is a bird a Quadruped?", Quadruped.check(bird)); // => true
console.log("Is a dog a Biped?", Biped.check(dog)); // => true