instanceof, scopes and objects

instanceof, javascript, scope

Solution

You're explicitly returning an object from the `foo` function. That object is not an instance of `foo`. Hence `bar` is not an instance of `foo`. This is how I would rewrite your code:

var foo = fooFactory();

var bar = new foo;

console.log("is " + bar.getName() + " instance of foo: " +
    bar instanceof factory.foo);

function fooFactory() {
    return function () {
        var name = "foo object";

        this.getName = function () {
            return name;
        };
    };
}

The reason I would write it like this is as follows:

- A factory function should not be called with `new`. Only constructor functions should be called with `new`. Furthermore even if you do call `fooFactory` with `new` it would make absolutely no difference as you're explicitly returning an object literal anyway. In fact it would be slower.

- Instead of returning an object with the constructor function and another function which instantiates the constructor wouldn't it be better to simply return the newly created constructor itself? Since your factory is named `fooFactory` I would assume that it returns `foo` and not an object which has a `foo` property.

- If you're going to create a function and use it as a constructor then don't explicitly return an object from it. When you call a function using `new` JavaScript automatically creates a new instance of the `prototype` of that function and binds it to `this` inside the function. As long as you don't explicitly return an object from the constructor function `this` is returned automatically.

Hope that helps.

Problem

could anyone explain this behaviour to me, please? ``` 'use strict' var fooFactory = function() { function foo() { var name = "foo object"; function getName() { return name; } return { getName: getName } } function getFoo() { return new foo; } return { getFoo: getFoo, foo: foo } }; var factory = new fooFactory(); var bar = factory.getFoo(); console.log("is " + bar.getName() + " instance of foo: " + (bar instanceof factory.foo)); // outputs "is foo object instance of foo: false" ``` i don't understand, why the foo object is no instance of the foo constructor i declare inside the fooFactory.

Original source