Is It Possible For An Object To Also Be A Function?

In the vain of this question. Is it at all possible for an object to also be a function. For example I have the object person which is an instance of some object. Is it possible fo

Solution 1:

Short answer, No. Yes! See proxy solution below.

In section 9.2.1 of the spec it outlines Function objects' internal [[Call]] property that allows that object to be called as a function. There is currently no way I know of to modify that property, i.e. make an object into a function after its creation. It will be possible with a fully compliant implementation of ES 2015 to subclass Function and have callable objects (currently works in FF, for example). Even then, I didn't try anything more than making a paper-thin layer over the Function constructor itself. However, ES 2015 also includes Proxies, and one of the proxy traps is 'apply'.

classPerson {
  constructor(arg, body) {
    this.fn = function(a) { this.a = a; };
    returnnewProxy(this, {
      apply: function(target, thisArg, args) {
        return target.fn.apply(target, args);
      }
    });
  }
}
var person = newPerson();
person(3);
person.a; //3

Tested in Chrome 49. Fails in FF unless Person extends Function and makes a call to super:

classPersonextendsFunction {
  constructor() {
    super();
    this.fn = function(a) { this.a = a; };
    returnnewProxy(this, {
      apply: function(target, thisArg, args) {
        return target.fn.apply(target, args);
      }
    });
  }
}
var person = newPerson();
person(3);
person.a;

According to MDN, the part about requiring the super call is correct at least (for subclasses) but I am unsure whether Proxies should let you call a non-function the way chrome lets you.

UPDATE

I opened another question about which behavior is correct. For those too lazy to follow a hyperlink the calling of a non-function is a bug in some specific versions of chrome that has since been fixed.