Javascript (ECMA-6) class magic method __call like PHP

There are no special __methods() in Javascript like in PHP, so all you have are those getters, setters, toString() and valueOf().

You could give Object.defineProperty() a shot, because with that you can dynamically create getters like so:

Object.defineProperty(obj, 'first_name', {
   get: function () { return … }
});

mdn

The result is similar to:

var obj = {
  get first_name () { return … }
}

If you need to call method of an object, you can also do it like that:

var prop = 'getFirstName',
    result = obj[prop]();

What also can be done in a for loop.

You can use a proxy to detect access to a property that your object does not have, and deal with it -- this comes close to PHP's __call:

var person = new Person();
// Wrap the object in a proxy
var person = new Proxy(person, {
    get: function(person, field) {
        if (field in person) return person[field]; // normal case
        console.log("Access to non-existent property '" + field + "'");
        // Check some particular cases:
        if (field == 'first_name') return person.getFirstName;
        // ...
        // Or other cases:
        return function () {
            // This function will be executed when property is accessed as a function
        }
    }
});

You could even do this in the constructor of your class:

class Person {
    constructor(data) {
        this.init(data);
        return new Proxy(this, {
            get: function(person, field) {
                if (field in person) return person[field]; // normal case
                console.log("Access to non-existent property '" + field + "'");
                // Check some particular cases:
                if (field == 'first_name') return person.getFirstName;
                // ...
                // Or other cases:
                return function () {
                    // This function will be executed when property is accessed as a function
                    return 15; // example
                }
            }
        });
    }
    // other methods ...
    //
}

The nice thing about proxies is that the returned object is still considered an instance of the original class. With the above code, the following will be true:

new Person() instanceof Person