Errata

In the test('With var.' ...

ok( !x, 'x should not pollute the global scope.');

This test dies in qunit v 1.11.0 because x is not defined. The test that worked for me is:

equals(typeof x === "undefined", 'x should not pollute the global scope');

Correction to previous erratum submission:


the test that works is:

test('With var' ...

equal(typeof x, "undefined", 'x should not pollute the global scope');

I'm reading the digital preview available in HTML format at
http://chimera.labs.oreilly.com/books/1234000000262/ch03.html

In the Chapter 3 (Functions), minimize side effects sections, I see the following:

> At this point, cart.items is a reference to the prototype items attribute. This is improved with one small change to the code:

I think that sentences is wrong, and is also misleading. At that point, cartProto.items is:

cartProto.items === []

the problem is that

savedCart.tems === cart.items

If you want to show the problems that might arise when inadvertently accessing the protoype properties you could use the addItem directly.

You could modify the example like this

createCart = function (items) {
return Object.create(cartProto);
}

session = {
get: function get() {
return this.cart;
},
// Grab the saved cart.
cart: createCart()
};

// create another cart instance,
// to show that they both point to the prototype's items array
anotherCart = createCart(),

// addItem gets triggered by an event handler somewhere:
session.cart.addItem('grapefruit');

ok(session.cart.items.indexOf('grapefruit')
!== -1, 'Passes: Session cart has grapefruit.');

ok(anotherCart.items.indexOf('grapefruit') === -1,
'Fails: A different cart is unchanged.');

ok(session.cart.items !== anotherCart.items),
'Fails: Each instance should have their own items.');

ok(session.cart.items !== cartProto.items),
'Fails: Each instance should shadow the prototype\'s items array.');

ok(anotherCart.items !== cartProto.items),
'Fails: Each instance should shadow the prototype\'s items array.');

--

I wrote an article with a bit more complicated example

http://opensas.wordpress.com/2013/06/09/troubleshooting-javascript-humble-homage-to-wat/

The sample code, which is supposed to be erroneous, looks correct; it already contains the call to bind() which the text says needs to be added. Also, the indentation of the code doesn't match the brackets.

The dot notation sample invokes the function and the square bracket notation returns the function itself.

...

Method invocation applies the function to the object to which it is attached. It takes the
form, object.methodName() (dot notation) or object['methodName'] (square bracket
notation).

...