Aliasing "namespaces" in JavaScript--why do we need to import symbols into a new namespace?

[Ray]

Hello,

I'm reading Mr. Flanagan's JS Definitive Guide 5th edition. I was
wondering about a point he make in section 10.2 of the book: "Importing
Symbols from Namespaces".

He mentions in there that one can create an alias for the symbol
defined in a namespace like this:

// This is an easier name, to save typing.
var define = com.davidflanagan.Class.define;

Another way of doing it, again from the same section, is discussed
next:

// Create a simple namespace. No error checking required. The
// module user knows that this symbol does not exist yet.
var Class = {};
// Now import a symbol into this new namespace.
Class.define = com.davidflanagan.Class.define;

Now my question is: what's wrong with aliasing the namespace itself?
E.g.:

var cls = com.davidflanagan.Class;
cls.define();

Why does he need to create a new simple namespace and import the symbol
from one namespace to another? Am I missing something really obvious
here?

Thanks,
Ray

 

[Peter Michaux]

Hello,

I'm reading Mr. Flanagan's JS Definitive Guide 5th edition. I was
wondering about a point he make in section 10.2 of the book: "Importing
Symbols from Namespaces".

He mentions in there that one can create an alias for the symbol
defined in a namespace like this:

// This is an easier name, to save typing.
var define = com.davidflanagan.Class.define;

Another way of doing it, again from the same section, is discussed
next:

// Create a simple namespace. No error checking required. The
// module user knows that this symbol does not exist yet.
var Class = {};
// Now import a symbol into this new namespace.
Class.define = com.davidflanagan.Class.define;

Now my question is: what's wrong with aliasing the namespace itself?
E.g.:

var cls = com.davidflanagan.Class;
cls.define();

Why does he need to create a new simple namespace and import the symbol
from one namespace to another? Am I missing something really obvious
here?

It looks like he wants to protect the original namespace. For example

var com = {davidflanagan:{Class:{}}};
com.davidflanagan.Class.foo = function() {alert('foo');};
var cls = com.davidflanagan.Class;
cls.foo = function(){alert('bar');};
com.davidflanagan.Class.foo(); // shows "bar" but maybe should be
"foo"

with Flanagan's importing system

var com = {davidflanagan:{Class:{}}};
com.davidflanagan.Class.foo = function() {alert('foo');};
var cls = {};
cls.foo = com.davidflanagan.Class.foo; // import one symbol
cls.foo = function(){alert('bar')}; // subsequently change it in the
new namespace
com.davidflanagan.Class.foo(); // shows "foo", so original namespace
not affected.

I'm just guessing on his intent.

Peter