Typescript @timestampable annotation

timestampable.ts

@timestampable
class Dog {
    public name: string = 'Paul';
}

function timestampable(func) {
    return <any>(function() {
        var genericConstructor = () => {};
        genericConstructor.prototype = func.prototype;
        var instance = new genericConstructor();

        func.apply(instance, <any>arguments);

        instance.createdAt = new Date();

        (<any>Object).observe(instance, (changes) => {
            if (changes.length == 1 && changes[0].name == 'updatedAt') {
                return;
            }

            instance.updatedAt = new Date();
        });

        return instance;
    });
}

// create my dog
var d = new Dog();
console.log(d.name, (<any>d).createdAt, (<any>d).updatedAt);

// change his name in 100ms
setTimeout(() => {
    d.name = 'Pierre';

    // let time for updatedAt to be computed and print next tick
    setTimeout(() => {
        console.log(d.name, (<any>d).createdAt, (<any>d).updatedAt);
    });
}, 100);

That's really creative!