How to properly extend ES6 Map

I have a simple case: a ES6 Map, and I need to add custom get() and set() to it.

But Map is a built-in object, so I'm not sure whether there would be any caveats in doing so. I've tried to search whether it is correct to subclass a Map, and got inconsistent results: it is unclear whether it's allowed by specification, what browser/node.js versions support it, and what side-effects are possible (and what to cover with tests).

As I understand, there are three main approaches to extend Map functionality:

1. Subclass it. That I've done, and it seems like it works.

class CustomMap extends Map{    get(key){        return super.get(key);    }    set(key, value){        return super.set(key, value);    }}

Problem with it: a lot of articles on the Internet state that you can run into troubles with extending built-in objects. Most are early 2016, and now is late 2017, testing in Chrome 61. Maybe now it is a safe and supported way of doing it?

2. Make a wrapper object

const Wrapper = function(){    this._map = new Map();    this.get = (key) => {return this._map.get(key);}    this.set = (key, value) => {this._map.set(key, value);}    ... everything else}

The least elegant solution, as I need to implement not just get and set, but all of Map functionality. Also, Wrapper is not an instance of Map.

3. Use ES6 Proxy

const ProxyMap = function(){    return new Proxy(new Map(), {        get(target, key){            return target.get(key)        }        set(target, key, value){            target.set(key, value);        }    }}

As with extending a class, it is unadvisable to apply Proxy to some built-in types. But again, a lot of time passed since introducing the Proxy specifications; maybe now Map could by proxied in modern browsers?

So, the question is: what way of extending a Map is a correct and robust way in 2017?