decorate.js

/*
* 装饰者模式
* */
"use strict";

function decorate(component) {
    const proto = Object.getPrototypeOf(component);

    function Decorator(component) {
        this.component = component;
    }

    Decorator.prototype = Object.create(proto);

    //new method
    Decorator.prototype.greetings = function () {
        return 'Hi!';
    };

    //delegated method
    Decorator.prototype.hello = function () {
        return this.component.hello.apply(this.component, arguments);
    };

    return new Decorator(component);
}

class Greeter {
    hello(subject) {
        return `Hello ${subject}`;
    }
}

const decoratedGreeter = decorate(new Greeter());
console.log(decoratedGreeter.hello('world')); // uses original method
console.log(decoratedGreeter.greetings()); // uses new method