How to emulate the php __call method in JavaScript

__call-in-javascript.js

/**
 * PHP's __call magic method is pretty useful. Unfortunately 
 * there is no equivalent in JavaScript, but it can be 
 * emulated with Proxy:
 */

magicMethodsProxy = 
{
    get: function(target, prop, receiver) 
    {
        // Does prop exists? Is it a method?
        if (target[prop] != undefined && typeof target[prop] == 'function') {
            // Wrap it around a function and return it
            return function(...args) 
            {
                // in order to preserve the default arguments the method may have, we pass undefined
                // instead of an empty arguments object
                var value = target[prop].apply(target, (args.length ? args : undefined) );
                // it is important to return the proxy instead of the target in order to make 
                // future calls to this method
                return value == target ? this : value;
            }
        }

        // Does prop exists?
        if (target[prop] != undefined) {
            return target[prop];
        }

        // Falls to __call
        return function(...args) 
        {
            return target.__call(prop, args, this);
        };
    }
}

/*---------------------------*/

class Music 
{
    constructor(file) 
    {
        this.file           = file;
        this.currentTime    = 0;
        this.metadata       = 
        {
            title : '', 
            artist: '', 
            lyrics: ''
        };

        // return the proxy
        return new Proxy(this, magicMethodsProxy);
    }

    __call(method, args, proxy) 
    {
        if (this.metadata[method] == undefined) {
            throw 'Method "'+method+'" is undefined';
        }

        this.metadata[method] = args[0];
        // again, it is important to return the proxy 
        // instead of the target
        return proxy;
    }

    play(seconds = 0) 
    {
        this.seconds = seconds;
        return this;
    }
}

/*---------------------------*/

var music = new Music('the-bards-song-the-hobbit.mp3');

music.play(50)                          // an actual method
.title("The Bard's song: The Hobbit")   // not a method
.artist("Blind Guardian")
.lyrics(`Out in the distance
There's so much gold
The treasure that I've found
Is more than enough
Far to the hill we've to go
Over the moutains and ...`);

console.log(music.seconds);         // 50
console.log(music.metadata.title);  // The Bard's song: The Hobbit
music.blindGuardianSux('just kiding, it is awesome.'); // throw exception