Question

I saw this article on polymorphic callable objects and was trying to get it to work, however it seems that they are not really polymorphic, or at least they do not respect the prototype chain.

This code prints undefined, not "hello there".

Does this method not work with prototypes, or am I doing something wrong?

var callableType = function (constructor) {
  return function () {
    var callableInstance = function () {
      return callableInstance.callOverload.apply(callableInstance, arguments);
    };
    constructor.apply(callableInstance, arguments);
    return callableInstance;
  };
};

var X = callableType(function() {
    this.callOverload = function(){console.log('called!')};
});

X.prototype.hello = "hello there";

var x_i = new X();
console.log(x_i.hello);

Answer 1

You’d need to change this:

var X = callableType(function() {
    this.callOverload = function(){console.log('called!')};
});

to this:

var X = new (callableType(function() {
    this.callOverload = function(){console.log('called!')};
}));

Notice the new as well as the parentheses around the callableType invocation.

The parentheses allows callableType to be invoked and return the function, which is used as the constructor for new.

---

EDIT:

var X = callableType(function() {
    this.callOverload = function() {
        console.log('called!')
    };
});

var someType = X();      // the returned constructor is referenced
var anotherType = X();   // the returned constructor is referenced

someType.prototype.hello = "hello there";  // modify the prototype of
anotherType.prototype.hello = "howdy";     //    both constructors

var some_i = new someType();           // create a new "someType" object
console.log(some_i.hello, some_i);

var another_i = new anotherType();     // create a new "anotherType" object
console.log(another_i.hello, another_i);

someType();      // or just invoke the callOverload
anotherType();

I really don’t know how/where/why you’d use this pattern, but I suppose there’s some good reason.