deco.js

"use strict";

function loggableClass(target) {
    console.log("Class: %s", target.name);

    return target;
}

function loggableMethod(target, name, descriptor) {
    console.log("Method: %s", name);

    return descriptor;
}

@loggableClass
class Klass {
    @loggableMethod
    hello() {
        console.log("world");
    }
}