Namespaces can be found in almost any serious JavaScript application. Unless weâre working with a simple code snippet, itâs imperative that we do our best to ensure that weâre implementing namespacing correctly, as itâs not just simple to pick up, itâll also avoid third-party code clobbering our own. The patterns weâll be examining in this section are:
Single global variables
Prefix namespacing
Object literal notation
Nested namespacing
Immediately-invoked Function
Expressions
Namespace injection
One popular pattern for namespacing in JavaScript is opting for a single global variable as our primary object of reference. A skeleton implementation of this where we return an object with functions and properties can be found below:
var
myApplication
=
(
function
()
{
function
(){
//...
},
return
{
//...
}
})();
Although this works for certain situations, the biggest challenge with the single global variable pattern is ensuring that no one else has used the same global variable name as we have in the page.
One solution to the above problem, as mentioned by Peter
Michaux, is to use prefix namespacing. Itâs a simple concept at
heart, but the idea is we select a unique prefix namespace we wish to
use (in this example, myApplication_
)
and then define any methods, variables, or other objects after the
prefix as follows:
var
myApplication_propertyA
=
{};
var
myApplication_propertyB
=
{};
function
myApplication_myMethod
(){
//...
}
This is effective from the perspective of decreasing the chances of a particular variable existing in the global scope, but remember that a uniquely named object can have the same effect.
This aside, the biggest issue with the pattern is that it can result in a large number of global objects once our application starts to grow. There is also quite a heavy reliance on our prefix not being used by any other developers in the global namespace, so be careful if opting to use this.
For more on Peterâs views about the single global variable pattern, read his excellent post on them: http://michaux.ca/articles/javascript-namespacing.
Object literal notation, which we also cover in the Module pattern section, can be thought of as an object containing a collection of key-value pairs with a colon separating each pair of keys and values, where keys can also represent new namespaces.
var
myApplication
=
{
// As we've seen, we can easily define functionality for
// this object literal..
getInfo
:
function
(){
//...
},
// but we can also populate it to support
// further object namespaces containing anything
// anything we wish:
models
:
{},
views
:
{
pages
:
{}
},
collections
:
{}
};
One can also opt for adding properties directly to the namespace:
myApplication
.
foo
=
function
(){
return
"bar"
;
}
myApplication
.
utils
=
{
toString
:
function
(){
//...
},
export
:
function
(){
//...
}
}
Object literals have the advantage of not polluting the global namespace but assist in organizing code and parameters logically. They are truly beneficial if you wish to create easily readable structures that can be expanded to support deep nesting. Unlike simple global variables, object literals often also take into account tests for the existence of a variable by the same name, so the chances of collision occurring are significantly reduced.
The next sample demonstrates a number of different ways in which you can check to see if an object namespace already exists, defining it if it doesnât.
// This doesn't check for existence of "myApplication" in
// the global namespace. Bad practice as we can easily
// clobber an existing variable/namespace with the same name
var
myApplication
=
{};
// The following options *do* check for variable/namespace existence.
// If already defined, we use that instance, otherwise we assign a new
// object literal to myApplication.
//
// Option 1: var myApplication = myApplication || {};
// Option 2 if( !MyApplication ){ MyApplication = {} };
// Option 3: window.myApplication || ( window.myApplication = {} );
// Option 4: var myApplication = $.fn.myApplication = function() {};
// Option 5: var myApplication = myApplication === undefined ? {} : myApplication;
Youâll often see developers opting for Option 1 or Option 2âthey are both straightforward and are equivalent in terms of their end result.
Option 3 assumes that youâre working in the global namespace, but it can also be written as:
myApplication
||
(
myApplication
=
{});
This variation assumes that myApplication
has
already been initialized, so itâs only really useful for a
parameter/argument scenario, as in the following example:
function foo() { myApplication || ( myApplication = {} ); } // myApplication hasn't been initialized, // so foo() throws a ReferenceError foo(); // However accepting myApplication as an // argument function foo( myApplication ) { myApplication || ( myApplication = {} ); } foo(); // Even if myApplication === undefined, there is no error // and myApplication gets set to {} correctly
Options 4 can be useful for writing jQuery plug-ins where:
// If we were to define a new plug-in.. var myPlugin = $.fn.myPlugin = function() { ... }; // Then later rather than having to type: $.fn.myPlugin.defaults = {}; // We can do: myPlugin.defaults = {};
This results in better compression (minification) and can save on scope lookups.
Option 5 is a little similar to Option 4, but is a long form that
evaluates whether myApplication
is
undefined
inlineâsuch that itâs defined as an object
if notâand set to an existing value for myApplication
if so.
It is shown just for the sake of being thorough, but in most situations, Options 1â4 will more than suffice for most needs.
There is, of course, a great deal of variance in how and where object literals are used for organizing and structuring code. For smaller applications wishing to expose a nested API for a particular self-enclosed module, you may just find yourself using the Revealing Module pattern, which we covered earlier in the book:
var namespace = (function () { // defined within the local scope var privateMethod1 = function () { /* ... */ }, privateMethod2 = function () { /* ... */ } privateProperty1 = "foobar"; return { // the object literal returned here can have as many // nested depths as we wish, however as mentioned, // this way of doing things works best for smaller, // limited-scope applications in my personal opinion publicMethod1: privateMethod1, // nested namespace with public properties properties:{ publicProperty1: privateProperty1 }, // another tested namespace utils:{ publicMethod2: privateMethod2 } ... } })();
The benefit of using object literals here is that they offer us a very elegant key/value syntax to work with; one where weâre able to easily encapsulate any distinct logic or functionality for our application in a way that clearly separates it from others and provides a solid foundation for extending our code.
var
myConfig
=
{
language
:
"english"
,
defaults
:
{
enableGeolocation
:
true
,
enableSharing
:
false
,
maxPhotos
:
20
},
theme
:
{
skin
:
"a"
,
toolbars
:
{
index
:
"ui-navigation-toolbar"
,
pages
:
"ui-custom-toolbar"
}
}
}
Note that JSON is a subset of object literal notation, and there are really only minor syntactical differences between it and the above (e.g., JSON keys must be strings). If, for any reason, one wishes to use JSON for storing configuration data instead (e.g., for simpler storage when sending to the backend), feel free to. For more on the object literal pattern, I recommend reading Rebecca Murpheyâs excellent article on the topic, as she covers a few areas we didnât touch upon.
An extension of the object literal pattern is nested namespacing. Itâs another common pattern used that offers a lower risk of collision due to the fact that even if a namespace already exists, itâs unlikely the same nested children do.
Does this look familiar?
YAHOO
.
util
.
Dom
.
getElementsByClassName
(
"test"
);
Older versions of Yahoo!âs YUI library use the nested object namespacing pattern regularly. During my time as an engineer at AOL, we also used this pattern in many of our larger applications. A sample implementation of nested namespacing may look like this:
var
myApp
=
myApp
||
{};
// perform a similar existence check when defining nested
// children
myApp
.
routers
=
myApp
.
routers
||
{};
myApp
.
model
=
myApp
.
model
||
{};
myApp
.
model
.
special
=
myApp
.
model
.
special
||
{};
// nested namespaces can be as complex as required:
// myApp.utilities.charting.html5.plotGraph(/*..*/);
// myApp.modules.financePlanner.getSummary();
// myApp.services.social.facebook.realtimeStream.getLatest();
Note
The above differs from how YUI3 approaches namespacing as modules there use a sandboxed API host object with far less and far shallower namespacing.
We can also opt to declare new nested namespaces/properties as indexed properties as follows:
myApp
[
"routers"
]
=
myApp
[
"routers"
]
||
{};
myApp
[
"models"
]
=
myApp
[
"models"
]
||
{};
myApp
[
"controllers"
]
=
myApp
[
"controllers"
]
||
{};
Both options are readable, organized, and offer a relatively safe
way of namespacing our application in a similar fashion to what we may
be used to in other languages. The only real caveat, however, is that it
requires our browserâs JavaScript engine first locating the
myApp
object and then digging down until it gets to
the function we actually wish to use.
This can mean an increased amount of work to perform lookups; however, developers such as Juriy Zaytsev have previously tested and found the performance differences between single object namespacing versus the ânestedâ approach to be quite negligible.
Earlier in the book, we briefly covered the concept of an immediately invoked function expression; IIFE, which is effectively an unnamed function, immediately invoked after itâs been defined. If it sounds familiar itâs because you may have previous come across it referred to as a self-executing (or self-invoked) anonymous function, however I personally feel Ben Almanâs IIFE naming is more accurate. In JavaScript, because both variables and functions explicitly defined within such a context may only be accessed inside of it, function invocation provides an easy means to achieving privacy.
IIFEs are a popular approach to encapsulating application logic to protect it from the global namespace but also have their use in the world of namespacing.
Examples of IIFEs can be found below:
// an (anonymous) immediately-invoked function expression
(
function
()
{
/*...*/
})();
// a named immediately-invoked function expression
(
function
foobar
()
{
/*..*/
}());
// this is technically a self-executing function which is quite different
function
foobar
()
{
foobar
();
}
while a slightly more expanded version of the first example might look like:
var
namespace
=
namespace
||
{};
// here a namespace object is passed as a function
// parameter, where we assign public methods and
// properties to it
(
function
(
o
){
o
.
foo
=
"foo"
;
o
.
bar
=
function
(){
return
"bar"
;
};
})(
namespace
);
console
.
log
(
namespace
);
Whilst readable, this example could be significantly expanded on to address common development concerns such as defined levels of privacy (public/private functions and variables) as well as convenient namespace extension. Letâs go through some more code:
// namespace (our namespace name) and undefined are passed here
// to ensure 1. namespace can be modified locally and isn't
// overwritten outside of our function context
// 2. the value of undefined is guaranteed as being truly
// undefined. This is to avoid issues with undefined being
// mutable pre-ES5.
;(
function
(
namespace
,
undefined
)
{
// private properties
var
foo
=
"foo"
,
bar
=
"bar"
;
// public methods and properties
namespace
.
foobar
=
"foobar"
;
namespace
.
sayHello
=
function
()
{
speak
(
"hello world"
);
};
// private method
function
speak
(
msg
)
{
console
.
log
(
"You said: "
+
msg
);
};
// check to evaluate whether "namespace" exists in the
// global namespace - if not, assign window.namespace an
// object literal
}(
window
.
namespace
=
window
.
namespace
||
{}
));
// we can then test our properties and methods as follows
// public
// Outputs: foobar
console
.
log
(
namespace
.
foobar
);
// Outputs: hello world
namescpace
.
sayHello
();
// assigning new properties
namespace
.
foobar2
=
"foobar"
;
// Outputs: foobar
console
.
log
(
namespace
.
foobar2
);
Extensibility is of course key to any scalable namespacing pattern and IIFEs can be used to achieve this quite easily. In the below example, our ânamespaceâ is once again passed as an argument to our anonymous function and is then extended (or decorated) with further functionality:
// let's extend the namespace with new functionality
(
function
(
namespace
,
undefined
){
// public method
namespace
.
sayGoodbye
=
function
()
{
console
.
log
(
namespace
.
foo
);
console
.
log
(
namespace
.
bar
);
speak
(
"goodbye"
);
}
}(
window
.
namespace
=
window
.
namespace
||
{});
// Outputs: goodbye
namespace
.
sayGoodbye
();
If you would like to find out more about this pattern, I recommend reading Benâs IIFE post for more information.
Namespace injection is another variation on the IIFE in
which we âinjectâ the methods and properties for a specific namespace
from within a function wrapper using this
as a
namespace proxy. The benefit this pattern offers is easy application of
functional behavior to multiple objects or namespaces and can come in
useful when applying a set of base methods to be built on later (e.g.,
getters and setters).
The disadvantages of this pattern are that there may be easier or more optimal approaches to achieving this goal (e.g., deep object extension or merging), which I cover earlier in the section.
Below we can see an example of this pattern in action, where we
use it to populate the behavior for two namespaces: one initially
defined (utils
) and another which we dynamically
create as a part of the functionality assignment for
utils
(a new namespace called
tools
).
var
myApp
=
myApp
||
{};
myApp
.
utils
=
{};
(
function
()
{
var
val
=
5
;
this
.
getValue
=
function
()
{
return
val
;
};
this
.
setValue
=
function
(
newVal
)
{
val
=
newVal
;
}
// also introduce a new sub-namespace
this
.
tools
=
{};
}).
apply
(
myApp
.
utils
);
// inject new behaviour into the tools namespace
// which we defined via the utilities module
(
function
()
{
this
.
diagnose
=
function
(){
return
"diagnosis"
;
}
}).
apply
(
myApp
.
utils
.
tools
);
// note, this same approach to extension could be applied
// to a regular IIFE, by just passing in the context as
// an argument and modifying the context rather than just
// "this"
// Usage:
// Outputs our populated namespace
console
.
log
(
myApp
);
// Outputs: 5
console
.
log
(
myApp
.
utils
.
getValue
()
);
// Sets the value of `val` and returns it
myApp
.
utils
.
setValue
(
25
);
console
.
log
(
myApp
.
utils
.
getValue
()
);
// Testing another level down
console
.
log
(
myApp
.
utils
.
tools
.
diagnose
()
);
Angus Croll has also suggested the idea of using the call API to provide a natural separation between contexts and arguments previously. This pattern can feel a lot more like a module creator, but as modules still offer an encapsulation solution, weâll briefly cover it for the sake of thoroughness:
// define a namespace we can use later
var
ns
=
ns
||
{},
ns2
=
ns2
||
{};
// the module/namespace creator
var
creator
=
function
(
val
){
var
val
=
val
||
0
;
this
.
next
=
function
()
{
return
val
++
};
this
.
reset
=
function
()
{
val
=
0
;
}
}
creator
.
call
(
ns
);
// ns.next, ns.reset now exist
creator
.
call
(
ns2
,
5000
);
// ns2 contains the same methods
// but has an overridden value for val
// of 5000
As mentioned, this type of pattern is useful for assigning a similar base set of functionality to multiple modules or namespaces. I would however only really suggest using it where explicitly declaring functionality within an object/closure for direct access doesnât make sense.
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