Dynamic delegation inheritance

Question

Let's say I have constructor functions Foo, Bar and Qux. How can I create a new object with a delegation chain (using those constructors) that I would dynamically choose on the fly ?

For example, an object would have the delegation chain Foo -> Bar.
Another object would have the chain Foo -> Qux.

function Foo() {
  this.foo = function() {
    console.log('foo');
  }
}

function Bar() {
  this.bar = function() {
    console.log('bar');
  }
}

function Qux() {
  this.qux = function() {
    console.log('qux');
  }
}

An object fooBar would be able to call foo() and bar(). Another object fooQux would be able to call foo() and qux(). Etc.

Answer 1

You can use those constructors as mixins:

var fooBar = {};
Bar.call(fooBar);
Foo.call(fooBar);

var fooQux = {};
Qux.call(fooQux);
Foo.call(fooQux);

But you might want to write them as decorators, maybe even returning the modified object, not as constructors, because you cannot use their prototypes anyway. So a more convenient pattern would be

function withFoo(obj) {
  obj.foo = function() {
    console.log('foo');
  };
  return obj;
}

function withBar(obj) {
  obj.bar = function() {
    console.log('bar');
  };
  return obj;
}

function withQux(obj) {
  obj.qux = function() {
    console.log('qux');
  };
  return obj;
}

so that you can use them like

var fooBar = withFoo(withBar({}));
var fooQux = withFoo(withQux({}));