How do I declare a namespace in JavaScript?
Asked Answered
A

29

1078

How do I create a namespace in JavaScript so that my objects and functions aren't overwritten by other same-named objects and functions? I've used the following:

if (Foo == null || typeof(Foo) != "object") { var Foo = new Object();}

Is there a more elegant or succinct way of doing this?

Afteryears answered 19/5, 2009 at 8:11 Comment(6)
I can see where you're going with the checking to see if the namespace is taken, but since the object will not be created if this fails I think the better approach is to alert if the namespace is taken. Frankly this should just not happen in most JS situations and should be caught quickly in development.Thaw
Take a top-level "namespace" (window property). Own it. Conflicts should be detected early on in testing. Don't bother adding all these "what if" checks. It's a fatal issue for duplicate "namespaces" and should be treated as such. You can follow an approach like jQuery to allow inhabiting a custom "namespace"; but this is still a design-time issue.Volitive
see also #2103091 for performance issuesStillborn
see also #4125979 for object vs function namespacesStillborn
This is a ton of information, but really lays out the differences amongst the different JS design patterns. It helped me a lot: addyosmani.com/resources/essentialjsdesignpatterns/bookValentine
Meh, nowadays we have symbols and modules, so duplicate namespaces shouldn’t even be an issue.Frentz
L
814

I like this:

var yourNamespace = {

    foo: function() {
    },

    bar: function() {
    }
};

...

yourNamespace.foo();
Lazulite answered 19/5, 2009 at 8:22 Comment(11)
The important point is to be religious about expanding no further than the one root variable. Everything must flow from this.Thaw
The syntax of this approach really bothers me. I hate not ending lines with a semicolon and in this solution declaration order matters. I do still think it's a completely valid and in cases a good solution. How do you do callback functions on a JQUery call with this approach?Thriller
I have a problem making this kind of namespace work with IE7, as posted here: #4492872 - not sure whether it has anything to do with the namespace declaration though. It works fine in all "standard" browsers including IE8Colp
This does not create a closure for your code - it makes it tedious to call your other functions because they always have to look like: yourNamespace.bar(); I made an open source project JUST to address this design problem: github.com/mckoss/namespace.Auriol
annakata: "The important point is to be religious about expanding no further than the one root variable."- Why is this?Undertone
@user406905: Because then you'd have two global identifiers, everything should live under the one namespace.Azriel
@alex: I can't speak for user406905, but my interpretation of what annakata said is that you should have the one "level" of properties and methods underneath the root namespace. In other words, do me.myselfAndI rather than me.myself.and.i so you have as shallow an object structure as possible. Of course I might have misinterpreted this.Phloem
@Azriel - why should there be a shallow object structure?Madonia
@Madonia I meant that everything should be under MyApp, e.g. MyApp.Views.Profile = {} rather than MyApp.users = {} and MyViews.Profile = {}. Not necessarily that there should only be two levels depth.Azriel
It's worth wrapping yourNamespace in a lexical closure.Suffering
@Undertone The big reason of namespaces is to minimize the chance of name collisions in the future within the global namespace that all code share. The key is to pollute the global namespace the least possible with local/custom variables, to avoid name collisions in the future, which are hard to troubleshoot and quickly becomes a mess. So the tradeoff is all your local variables will reside in that one namespace. And try to give it a name that hopefully another component will not use one day. That's what this best practice is about.Thayne
S
1076

I use the approach found on the Enterprise jQuery site:

Here is their example showing how to declare private & public properties and functions. Everything is done as a self-executing anonymous function.

(function( skillet, $, undefined ) {
    //Private Property
    var isHot = true;

    //Public Property
    skillet.ingredient = "Bacon Strips";

    //Public Method
    skillet.fry = function() {
        var oliveOil;

        addItem( "\t\n Butter \n\t" );
        addItem( oliveOil );
        console.log( "Frying " + skillet.ingredient );
    };

    //Private Method
    function addItem( item ) {
        if ( item !== undefined ) {
            console.log( "Adding " + $.trim(item) );
        }
    }
}( window.skillet = window.skillet || {}, jQuery ));

So if you want to access one of the public members you would just go skillet.fry() or skillet.ingredients.

What's really cool is that you can now extend the namespace using the exact same syntax.

//Adding new Functionality to the skillet
(function( skillet, $, undefined ) {
    //Private Property
    var amountOfGrease = "1 Cup";

    //Public Method
    skillet.toString = function() {
        console.log( skillet.quantity + " " +
                     skillet.ingredient + " & " +
                     amountOfGrease + " of Grease" );
        console.log( isHot ? "Hot" : "Cold" );
    };
}( window.skillet = window.skillet || {}, jQuery ));

The third undefined argument

The third, undefined argument is the source of the variable of value undefined. I'm not sure if it's still relevant today, but while working with older browsers / JavaScript standards (ecmascript 5, javascript < 1.8.5 ~ firefox 4), the global-scope variable undefined is writable, so anyone could rewrite its value. The third argument (when not passed a value) creates a variable named undefined which is scoped to the namespace/function. Because no value was passed when you created the name space, it defaults to the value undefined.

Summers answered 10/5, 2011 at 8:28 Comment(16)
+1 for this great sample. For anyone interested, this sample was part of Elijah Manor's excellent presentation at Mix 2011 (ignore the title) live.visitmix.com/MIX11/Sessions/Speaker/Elijah-ManorRodrigues
From Elijah's article, here are the pros and cons of this approach, paraphrased. Pros: 1. Public and private properties and methods, 2. doesn’t use cumbersome OLN, 3. Protects undefined 4. Ensures that $ refers to jQuery, 5. Namespace can span files, Cons: Harder to understand than OLNSeismography
Excellent. But it fails if jQuery is not already loaded. Is there a way to execute anyway, and in there to test for it and load if necessary?Klayman
@Klayman - Why would it fail? jQuery should be the dependency and should be loaded preceeding your scriptMadonia
@Ryan: I'm calling this from a bookmarklet where I don't test for jQuery (want to keep the bookmarklet as simple as possible, logic is done server-side). I overcame this by removing the $ parameter, and testing/loading for jQuery inside the namespace.Klayman
This is called today IIFE (Immediately Invoked Function Expression). Thanks for your answer +1!Cullum
@CpILL the third ùndefined` argument is for ensure that no else function will pass a third argument and will modify the behavior. It is a guaranty.Cullum
@CpILL: not sure if still relevant, but the third, undefined argument is source of the variable of value undefined. While working with older browsers / javascript standard (ecmascript 5, javascript < 1.8.5 ~ firefox 4), the global-scope variable undefined is writable, so anyone could rewrite its value. Adding third, additional argument you are not passing makes it value undefined, so you were creating namespace-scope undefined which won't be rewritten by outside sources.Alleman
So I don't really understand the purpose of window.skillet = window.skillet || {}. Why would you want another file to accidentally append to the definition of skillet? Wouldn't you rather it did so intentionally? I'd rather see a big bug pop up.... Perhaps it's for when people want to add extensions to your module but you don't know which one is loading first?Catsup
@SapphireSun: Who said it had to be by accident? The syntax allows you to extend the class in multiple places.Senator
If you feel confused, @Jared Beck presented an excellent pro/con breakdown of the article. Perhaps one additional Con: Don't use this just because it's better. The { } OLN (Object Literal Notation) as explained in the accepted answer is perfect for simple scenarios.Sarpedon
@Catsup The benefit of window.skillet = window.skillet || {} is that it permits multiple scripts to safely add to the same namespace when they don't know in advance in what order they will execute. This can be helpful either if you want to be able to reorder your script inclusions arbitrarily without breaking your code, or if you want to load scripts asynchronously with the async attribute and so have no guarantee about execution order. See #6440079Works
I was going to add an example as well; I commend you on this example code. @MarkAmery, I have to say that your comment is probably one of the most misunderstood components of javascript structures and you have provided an excellent explanation showing the scope of each function/variable and how to invoke them.Rinee
There is one more big downside (imho) with doing namespace.func = function(){ /* ... */};: All these functions end up being anonymous. It is an inconvenience when debugging, looking at stacktraces etc. Please consider to stop writing anonymous functions. (I am the author of that blog post).Darcydarda
The answer provided in this example has a bug - I can't find a solution for this. In the original implementation of skillet, a private variable isHot is declared. Subsequently, skillet is extended to add the toString() method, and in this extension the private variable toHot is referenced. In my tests, this is not possible, as the private variable from the original implementation can't be referenced in a subsequent extension. Paste the code from this answer into the JS console in your browser. skillet.toString() fails: ReferenceError: Can't find variable: isHotHawsepipe
@Hawsepipe The full example on the site referenced in the answer shows that causes an error. The benefit is you can create a second closure? to extend the namespace but the closures still can't access the private variables of the other, but that also means you don't have to worry about your private variables conflicting with those in the other. (I'm just starting to understand this, so may have some of that wrong.)Metrify
L
814

I like this:

var yourNamespace = {

    foo: function() {
    },

    bar: function() {
    }
};

...

yourNamespace.foo();
Lazulite answered 19/5, 2009 at 8:22 Comment(11)
The important point is to be religious about expanding no further than the one root variable. Everything must flow from this.Thaw
The syntax of this approach really bothers me. I hate not ending lines with a semicolon and in this solution declaration order matters. I do still think it's a completely valid and in cases a good solution. How do you do callback functions on a JQUery call with this approach?Thriller
I have a problem making this kind of namespace work with IE7, as posted here: #4492872 - not sure whether it has anything to do with the namespace declaration though. It works fine in all "standard" browsers including IE8Colp
This does not create a closure for your code - it makes it tedious to call your other functions because they always have to look like: yourNamespace.bar(); I made an open source project JUST to address this design problem: github.com/mckoss/namespace.Auriol
annakata: "The important point is to be religious about expanding no further than the one root variable."- Why is this?Undertone
@user406905: Because then you'd have two global identifiers, everything should live under the one namespace.Azriel
@alex: I can't speak for user406905, but my interpretation of what annakata said is that you should have the one "level" of properties and methods underneath the root namespace. In other words, do me.myselfAndI rather than me.myself.and.i so you have as shallow an object structure as possible. Of course I might have misinterpreted this.Phloem
@Azriel - why should there be a shallow object structure?Madonia
@Madonia I meant that everything should be under MyApp, e.g. MyApp.Views.Profile = {} rather than MyApp.users = {} and MyViews.Profile = {}. Not necessarily that there should only be two levels depth.Azriel
It's worth wrapping yourNamespace in a lexical closure.Suffering
@Undertone The big reason of namespaces is to minimize the chance of name collisions in the future within the global namespace that all code share. The key is to pollute the global namespace the least possible with local/custom variables, to avoid name collisions in the future, which are hard to troubleshoot and quickly becomes a mess. So the tradeoff is all your local variables will reside in that one namespace. And try to give it a name that hopefully another component will not use one day. That's what this best practice is about.Thayne
D
357

Another way to do it, which I consider it to be a little bit less restrictive than the object literal form, is this:

var ns = new function() {

    var internalFunction = function() {

    };

    this.publicFunction = function() {

    };
};

The above is pretty much like the module pattern and whether you like it or not, it allows you to expose all your functions as public, while avoiding the rigid structure of an object literal.

Debunk answered 19/5, 2009 at 8:39 Comment(12)
It's kind of blindsided me that anyone wouldn't love OLN. I just... what's not to love? What's so rigid?Thaw
1. There's a difference between OLN and the module pattern. 2. I don't /always/ like OLN as you have to remember to not put the last trailing comma and all your attributes must be initialized with a value (like null or undefined). Also, if you need closures for member functions, you will need small function factories for each of those methods. Another thing is that you must enclose all your control structures inside functions, whereas the above form does not impose that. That's not to say that I don't use OLN, is just that sometimes I don't like it.Marrow
this style is compatible with my javascript editor (eclipse), as in, it can do auto formatting and indentation.Annalee
I like this approach because it allows for private functions, variables, and pseudo-constants (i.e. var API_KEY = 12345;).Masonmasonic
I like this better than the comma separated object container that's voted higher. I don't see any shortcomings in comparison, either. Am I missing something?Cle
anybody knows why jQuery is not using this approach but the comma separated ?Commensurate
This pattern works for singleton objects, but jQuery is a constructor function. In my example you can't call ns(), and jQuery needs this.Marrow
Now if JSLint would not complain about this legit structure everything will be so much better :)Atchley
JS Newbie here... why is it that I don't have to type ns().publicFunction(), that is... ns.publicFunction() works.Haberdasher
@John Kraft, it's necause of the new keyword in front of the function keyword. Basically, what is doing is that it's declaring an anonymous function (and as a function, it is as well a constructor), and it then immediately invokes it as a constructor using new. As such, the final value that gets stored inside ns is an (unique) instance of that anonymous constructor. Hope it makes sense.Marrow
kind of a gotchya with this approach: if you want to access 'public' members or methods within an 'internal' method, you have to add on the 'class' name. Example: ns.publicFunction(); or ns.publicMember;Paediatrics
Also worth mentioning that in the above examples this refers to what you would expect in publicFunction, but refers to the global object in internalFunction. I usually add var self = this at the top to avoid confusion.Plumule
T
160

Is there a more elegant or succinct way of doing this?

Yes. For example:

var your_namespace = your_namespace || {};

then you can have

var your_namespace = your_namespace || {};
your_namespace.Foo = {toAlert:'test'};
your_namespace.Bar = function(arg) 
{
    alert(arg);
};
with(your_namespace)
{
   Bar(Foo.toAlert);
}
Tsosie answered 26/5, 2010 at 11:34 Comment(8)
this gives me an error in IE7. var your_namespace = (typeof your_namespace == "undefined" || !your_namespace ) ? {} : your_namespace ; works better.Allopathy
it should be var your_namespace = your_namespace = your_namespace || {} Works in every browser ;)Luanaluanda
+1 from me! Thin one works as Jaco Pretorius answer by expanding one library to different files or different places inside the same file. Just brilliant!Pestle
@Luanaluanda Can you please explain why it should be like this? var your_namespace = your_namespace = your_namespace || {}Comeuppance
What advantage would this have over var your_namespace = {};?Drooff
you would have the possibility to extend the your_namespace object in different js files. When using var your_namespace = {} you cannot do that, as the object will be overridden by each fileTsosie
This is the defacto "standard" way that commercial web development houses do this (from my experience). It's the clearest, most concise, most readable way of achieving the "namespace" paradigm within javascript as far as I'm concerned.Modiolus
And yet the MDN discourages the use of with?Metrify
B
97

I normally build it in a closure:

var MYNS = MYNS || {};

MYNS.subns = (function() {

    function privateMethod() {
        // Do private stuff, or build internal.
        return "Message";
    }

    return {
        someProperty: 'prop value',
        publicMethod: function() {
            return privateMethod() + " stuff";
        }
    };
})();

My style over the years has had a subtle change since writing this, and I now find myself writing the closure like this:

var MYNS = MYNS || {};

MYNS.subns = (function() {
    var internalState = "Message";

    var privateMethod = function() {
        // Do private stuff, or build internal.
        return internalState;
    };
    var publicMethod = function() {
        return privateMethod() + " stuff";
    };

    return {
        someProperty: 'prop value',
        publicMethod: publicMethod
    };
})();

In this way I find the public API and implementation easier to understand. Think of the return statement as being a public interface to the implementation.

Bargello answered 20/5, 2011 at 20:7 Comment(8)
Should you not check for MYNS.subns = MYNS.subns || {} ??Abm
A good point that should be the exercise to the developers intent. You need to consider what to do when it does exist, replace it, error, use existing or version check and conditionally replace. I've had differing situations that call for each variants. In most cases you possibly have this as a low risk edge case and replacing can be beneficial, consider a rogue module that tried to hijack the NS.Bargello
There is an explanation of this approach in the Book "Speaking Javascript" at page 412 if anyone has it, under the heading "Quick and Dirty Modules".Venterea
Will have to check it out. Was it talking negative due to the "dirty" in the heading? lolBargello
Optimization tip: while var foo = function and function foo are similar, being private; due to JavaScript's dynamically-typed nature, the latter is slightly faster as it skips a few instructions in most interpreters' pipelines. With var foo, the type system has to get invoked to find out what type is being assigned to said var, while with function foo, the type system automatically knows it's a function, so a couple function calls get skipped, which translates to fewer invocations of CPU instructions like jmp, pushq, popq, etc, which translates to a shorter CPU pipeline.Bullen
Also, I would argue that function foo is more readable than var foo = function, because even though the var syntax allows for vertical alignment, the function syntax is explicit, and immediately clear to a human reading the code. The var syntax leads to slightly longer mental parsing. So in a way, the function syntax optimizes for both CPU and brain pipelines. Neato! This is just a matter of taste, but the way I would have done that last snippet is like this: pastebin.com/Zkk49aj9. It's subtle, but I find it faster to read.Bullen
@B1KMusic that's both incorrect and poor advice. There's a distinct difference between the two. Using an assignment declares the function at runtime which allows delayed AND conditional function declarations, using function myFunc is defined at script evaluation and thus can not be declared conditionally. If you can any way prove your claims at efficiency then please provide it, you may find the opposite is true. For something defined only once it's not something you should be trying to optimise anyway.Bargello
@brett oops. You're right. I was thinking of a different scripting language. Though I still insist the function foo syntax is more readable. And I still like my version.Bullen
B
59

Because you may write different files of JavaScript and later combine or not combine them in an application, each needs to be able to recover or construct the namespace object without damaging the work of other files...

One file might intend to use the namespace namespace.namespace1:

namespace = window.namespace || {};
namespace.namespace1 = namespace.namespace1 || {};

namespace.namespace1.doSomeThing = function(){}

Another file might want to use the namespace namespace.namespace2:

namespace = window.namespace || {};
namespace.namespace2 = namespace.namespace2 || {};

namespace.namespace2.doSomeThing = function(){}

These two files can live together or apart without colliding.

Benco answered 9/11, 2010 at 4:27 Comment(2)
I've found this to be a very useful method for organizing client script into multiple files in large applications where functionality needs to be modular.Amadavat
Question asking specifically for multiple files: #5150624Foresight
C
54

Here's how Stoyan Stefanov does it in his JavaScript Patterns book which I found to be very good (it also shows how he does comments that allows for auto-generated API documentation, and how to add a method to a custom object's prototype):

/**
* My JavaScript application
*
* @module myapp
*/

/** @namespace Namespace for MYAPP classes and functions. */
var MYAPP = MYAPP || {};

/**
* A maths utility
* @namespace MYAPP
* @class math_stuff
*/
MYAPP.math_stuff = {

    /**
    * Sums two numbers
    *
    * @method sum
    * @param {Number} a First number
    * @param {Number} b Second number
    * @return {Number} Sum of the inputs
    */
    sum: function (a, b) {
        return a + b;
    },

    /**
    * Multiplies two numbers
    *
    * @method multi
    * @param {Number} a First number
    * @param {Number} b Second number
    * @return {Number} The inputs multiplied
    */
    multi: function (a, b) {
        return a * b;
    }
};

/**
* Constructs Person objects
* @class Person
* @constructor
* @namespace MYAPP
* @param {String} First name
* @param {String} Last name
*/
MYAPP.Person = function (first, last) {

    /**
    * First name of the Person
    * @property first_name
    * @type String
    */
    this.first_name = first;

    /**
    * Last name of the Person
    * @property last_name
    * @type String
    */
    this.last_name = last;
};

/**
* Return Person's full name
*
* @method getName
* @return {String} First name + last name
*/
MYAPP.Person.prototype.getName = function () {
    return this.first_name + ' ' + this.last_name;
};
Cambric answered 22/4, 2012 at 15:44 Comment(0)
F
33

I use this approach:

var myNamespace = {}
myNamespace._construct = function()
{
    var staticVariable = "This is available to all functions created here"

    function MyClass()
    {
       // Depending on the class, we may build all the classes here
       this.publicMethod = function()
       {
          //Do stuff
       }
    }

    // Alternatively, we may use a prototype.
    MyClass.prototype.altPublicMethod = function()
    {
        //Do stuff
    }

    function privateStuff()
    {
    }

    function publicStuff()
    {
       // Code that may call other public and private functions
    }

    // List of things to place publically
    this.publicStuff = publicStuff
    this.MyClass = MyClass
}
myNamespace._construct()

// The following may or may not be in another file
myNamespace.subName = {}
myNamespace.subName._construct = function()
{
   // Build namespace
}
myNamespace.subName._construct()

External code can then be:

var myClass = new myNamespace.MyClass();
var myOtherClass = new myNamepace.subName.SomeOtherClass();
myNamespace.subName.publicOtherStuff(someParameter);
Freshen answered 19/5, 2009 at 8:26 Comment(7)
Great detail! Thanks! Just wondering what's your take on Namespace.js. I've never used it myself, so I'm wondering if someone with your knowledge/skill/experience would consider using it.Euchre
I like it! On the other hand I get exception on first line of this external code, saying: 'myNameSpace.MyClass' [undefined] is not constructor. maybe it depends in JS implementation? :/Moluccas
@yossiba: Possibly. The code above is fairly standard stuff. In standard JS any function can be used as a constructor, there is nothing you need to do to mark a function as specifically for being used as a constructor. Are you using an unusual flavor like ActionScript or something?Freshen
@Anthony its better to use var MYNAMESPACE = MYNAMESPACE || {}; just using var myNamespace = {} is unsafe and moreover its better to declare your namespace in capsIntersect
@paul: "Better" can be quite subjective. I hate reading code that SHOUTS at me so I avoid using identifiers that use all uppercase. Whilst ns = ns || {} might seem more defensive it can lead to other unexpected results.Freshen
@Anthony its just an suggestion and following the conventions. Moreover, its all about your personal preference.Intersect
@AnthonyWJones, apart from mistakenly using an unintended variable, what unexpected results do you anticipate with ns = ns || {}? A more defensive approach could be var n = n && n.name === "NSNAME" ? n : { name: "NSNAME"};Bargello
H
32

This is a follow-up to user106826's link to Namespace.js. It seems the project moved to GitHub. It is now smith/namespacedotjs.

I have been using this simple JavaScript helper for my tiny project and so far it seems to be light yet versatile enough to handle namespacing and loading modules/classes. It would be great if it would allow me to import a package into a namespace of my choice, not just the global namespace... sigh, but that's besides the point.

It allows you to declare the namespace then define objects/modules in that namespace:

Namespace('my.awesome.package');
my.awesome.package.WildClass = {};

Another option is to declare the namespace and its contents at once:

Namespace('my.awesome.package', {
    SuperDuperClass: {
        saveTheDay: function() {
            alert('You are welcome.');
        }
    }
});

For more usage examples, look at the example.js file in the source.

Helprin answered 27/8, 2010 at 23:15 Comment(1)
As long as you remember this has some performance implications, as each time you access my.awesome.package.WildClass you're accessing the awesome property of my, the package property of my.awesome, and the WildClass property of my.awesome.package.Marked
C
29

Sample:

var namespace = {};
namespace.module1 = (function(){

    var self = {};
    self.initialized = false;

    self.init = function(){
        setTimeout(self.onTimeout, 1000)
    };

    self.onTimeout = function(){
        alert('onTimeout')
        self.initialized = true;
    };

    self.init(); /* If it needs to auto-initialize, */
    /* You can also call 'namespace.module1.init();' from outside the module. */
    return self;
})()

You can optionally declare a local variable, same, like self and assign local.onTimeout if you want it to be private.

Ceciliacecilio answered 10/5, 2012 at 11:44 Comment(0)
S
17

The Module pattern was originally defined as a way to provide both private and public encapsulation for classes in conventional software engineering.

When working with the Module pattern, we may find it useful to define a simple template that we use for getting started with it. Here's one that covers name-spacing, public and private variables.

In JavaScript, the Module pattern is used to further emulate the concept of classes in such a way that we're able to include both public/private methods and variables inside a single object, thus shielding particular parts from the global scope. What this results in is a reduction in the likelihood of our function names conflicting with other functions defined in additional scripts on the page.

var myNamespace = (function () {

  var myPrivateVar, myPrivateMethod;

  // A private counter variable
  myPrivateVar = 0;

  // A private function which logs any arguments
  myPrivateMethod = function( foo ) {
      console.log( foo );
  };

  return {

    // A public variable
    myPublicVar: "foo",

    // A public function utilizing privates
    myPublicFunction: function( bar ) {

      // Increment our private counter
      myPrivateVar++;

      // Call our private method using bar
      myPrivateMethod( bar );

    }
  };

})();

Advantages

why is the Module pattern a good choice? For starters, it's a lot cleaner for developers coming from an object-oriented background than the idea of true encapsulation, at least from a JavaScript perspective.

Secondly, it supports private data - so, in the Module pattern, public parts of our code are able to touch the private parts, however the outside world is unable to touch the class's private parts.

Disadvantages

The disadvantages of the Module pattern are that as we access both public and private members differently, when we wish to change visibility, we actually have to make changes to each place the member was used.

We also can't access private members in methods that are added to the object at a later point. That said, in many cases the Module pattern is still quite useful and when used correctly, certainly has the potential to improve the structure of our application.

The Revealing Module Pattern

Now that we're a little more familiar with the module pattern, let’s take a look at a slightly improved version - Christian Heilmann’s Revealing Module pattern.

The Revealing Module pattern came about as Heilmann was frustrated with the fact that he had to repeat the name of the main object when we wanted to call one public method from another or access public variables.He also disliked the Module pattern’s requirement for having to switch to object literal notation for the things he wished to make public.

The result of his efforts was an updated pattern where we would simply define all of our functions and variables in the private scope and return an anonymous object with pointers to the private functionality we wished to reveal as public.

An example of how to use the Revealing Module pattern can be found below

var myRevealingModule = (function () {

        var privateVar = "Ben Cherry",
            publicVar = "Hey there!";

        function privateFunction() {
            console.log( "Name:" + privateVar );
        }

        function publicSetName( strName ) {
            privateVar = strName;
        }

        function publicGetName() {
            privateFunction();
        }


        // Reveal public pointers to
        // private functions and properties

        return {
            setName: publicSetName,
            greeting: publicVar,
            getName: publicGetName
        };

    })();

myRevealingModule.setName( "Paul Kinlan" );

Advantages

This pattern allows the syntax of our scripts to be more consistent. It also makes it more clear at the end of the module which of our functions and variables may be accessed publicly which eases readability.

Disadvantages

A disadvantage of this pattern is that if a private function refers to a public function, that public function can't be overridden if a patch is necessary. This is because the private function will continue to refer to the private implementation and the pattern doesn't apply to public members, only to functions.

Public object members which refer to private variables are also subject to the no-patch rule notes above.

Sherillsherilyn answered 31/1, 2017 at 16:6 Comment(0)
R
17

If you need the private scope:

var yourNamespace = (function() {

  //Private property
  var publicScope = {};

  //Private property
  var privateProperty = "aaa"; 

  //Public property
  publicScope.publicProperty = "bbb";

  //Public method
  publicScope.publicMethod = function() {
    this.privateMethod();
  };

  //Private method
  function privateMethod() {
    console.log(this.privateProperty);
  }

  //Return only the public parts
  return publicScope;
}());

yourNamespace.publicMethod();

else if you won't ever use the private scope:

var yourNamespace = {};

yourNamespace.publicMethod = function() {
    // Do something...
};

yourNamespace.publicMethod2 = function() {
    // Do something...
};

yourNamespace.publicMethod();
Refrigeration answered 22/3, 2017 at 12:27 Comment(0)
C
15

You can declare a simple function to provide namespaces.

function namespace(namespace) {
    var object = this, tokens = namespace.split("."), token;

    while (tokens.length > 0) {
        token = tokens.shift();

        if (typeof object[token] === "undefined") {
            object[token] = {};
        }

        object = object[token];
    }

    return object;
}

// Usage example
namespace("foo.bar").baz = "I'm a value!";
Crabber answered 28/4, 2012 at 14:3 Comment(0)
A
10

I'm 7 years late to the party, but did quite a bit of work around this 8 years ago:

It is important to be able to easily and efficiently create multiple nested namespaces to keep a complex web application organized and manageable, while respecting the JavaScript global namespace (preventing namespace pollution), and with not clobbering any existing objects in the namespace path while doing so.

From the above, this was my circa-2008 solution:

var namespace = function(name, separator, container){
  var ns = name.split(separator || '.'),
    o = container || window,
    i,
    len;
  for(i = 0, len = ns.length; i < len; i++){
    o = o[ns[i]] = o[ns[i]] || {};
  }
  return o;
};

This isn't creating a namespace, but provides a function for creating namespaces.

This can be condensed to a minified one-liner:

var namespace=function(c,f,b){var e=c.split(f||"."),g=b||window,d,a;for(d=0,a=e.length;d<a;d++){g=g[e[d]]=g[e[d]]||{}}return g};

Example of use:

namespace("com.example.namespace");
com.example.namespace.test = function(){
  alert("In namespaced function.");
};

Or, as one statement:

namespace("com.example.namespace").test = function(){
  alert("In namespaced function.");
};

Either is then executed as:

com.example.namespace.test();

If you don't need support for legacy browsers, an updated version:

const namespace = function(name, separator, container){
    var o = container || window;
    name.split(separator || '.').forEach(function(x){
        o = o[x] = o[x] || {};
    });
    return o;
};

Now, I'd be leery of exposing namespace to the global namespace itself. (Too bad the base language doesn't provide this for us!) So I'd typically use this myself in a closure, such as:

(function(){
	const namespace = function(name, separator, container){
		var o = container || window;
		name.split(separator || '.').forEach(function(x){
			o = o[x] = o[x] || {};
		});
		return o;
	};
	const ns = namespace("com.ziesemer.myApp");
	
	// Optional:
	ns.namespace = ns;
	
	// Further extend, work with ns from here...
}());

console.log("\"com\":", com);

In a larger application, this only needs to be defined once at the beginning of a page load (for client-based web apps). Additional files can then reuse the namespace function if kept (included as "optional" in the above). At worst, if this function is re-declared a few times - it's only a few lines of code, and less if minified.

Adjudge answered 28/11, 2016 at 0:5 Comment(3)
This is great, but I have a question about let and const. Once you have created a namespace namespace("com.ziesemer.myApp"), is it possible to designate a property/object as const or let? Like com.ziesemer.myApp.logger - it seems to me that this can never be declared as const. I think with this I can't adopt some of those newer language features. Note: adopting the new Javascript modules is not an option unfortunately.Davidson
@Davidson - What you're looking for is not applicable here, as you're not strictly declaring variables - but new properties on to existing objects.Adjudge
yep. I realise that. The question was put to me by our architect, who is fighting me on the inclusion of this approach. He seems content with polluting the global namespace in the creaky, old, low quality code-base. Some people ¯_(ツ)_/¯Davidson
S
9

I created namespace which is inspired by Erlang's modules. It is a very functional approach, but that is how I write my JavaScript code these days.

It gives a closure a global namespace and exposes a defined set functions within that closure.

(function(){

  namespace("images", previous, next);
  // ^^ This creates or finds a root object, images, and binds the two functions to it.
  // It works even though those functions are not yet defined.

  function previous(){ ... }

  function next(){ ... }

  function find(){ ... } // A private function

})();
Scouring answered 4/7, 2010 at 4:25 Comment(0)
A
8

After porting several of my libraries to different projects, and having to constantly be changing the top level (statically named) namespace, I've switched to using this small (open source) helper function for defining namespaces.

global_namespace.Define('startpad.base', function(ns) {
    var Other = ns.Import('startpad.other');
    ....
});

Description of the benefits are at my blog post. You can grab the source code here.

One of the benefits I really like is isolation between modules with respect to load order. You can refer to an external module BEFORE it is loaded. And the object reference you get will be filled in when the code is available.

Auriol answered 27/3, 2010 at 6:38 Comment(2)
I've created an improved version (2.0) of the namespace library: code.google.com/p/pageforest/source/browse/appengine/static/src/…Auriol
all your links seems deadSlapstick
L
8

I use the following syntax for the namespace.

var MYNamespace = MYNamespace|| {};

 MYNamespace.MyFirstClass = function (val) {
        this.value = val;
        this.getValue = function(){
                          return this.value;
                       };
    }

var myFirstInstance = new MYNamespace.MyFirstClass(46);
alert(myFirstInstance.getValue());

jsfiddle: http://jsfiddle.net/rpaul/4dngxwb3/1/

Leavy answered 4/2, 2015 at 22:45 Comment(0)
E
6

I think you all use too much code for such a simple problem. No need to make a repo for that. Here's a single line function.

namespace => namespace.split(".").reduce((last, next) => (last[next] = (last[next] || {})), window);

Try it :

// --- definition ---
const namespace = name => name.split(".").reduce((last, next) => (last[next] = (last[next] || {})), window);

// --- Use ----
const c = namespace("a.b.c");
c.MyClass = class MyClass {};

// --- see ----
console.log("a : ", a);
Excitant answered 5/7, 2018 at 11:41 Comment(0)
T
5

ES6 Modules Namespace imports

// circle.js
export { name, draw, reportArea, reportPerimeter };
// main.js
import * as Circle from './modules/circle.js';

// draw a circle
let circle1 = Circle.draw(myCanvas.ctx, 75, 200, 100, 'green');
Circle.reportArea(circle1.radius, reportList);
Circle.reportPerimeter(circle1.radius, reportList);

This grabs all the exports available inside circle.js, and makes them available as members of an object Circle, effectively giving it its own namespace.

Troglodyte answered 24/9, 2021 at 9:25 Comment(0)
A
3

My favorite pattern has become lately this:

var namespace = (function() {
  
  // expose to public
  return {
    a: internalA,
    c: internalC
  }

  // all private
  
  /**
   * Full JSDoc
   */
  function internalA() {
    // ...
  }
  
  /**
   * Full JSDoc
   */
  function internalB() {
    // ...
  }
  
  /**
   * Full JSDoc
   */
  function internalC() {
    // ...
  }
  
  /**
   * Full JSDoc
   */
  function internalD() {
    // ...
  }
  
})();

Of course, return can be at the end, but if only function declarations follow it, it's much easier to see what's the namespace all about, and what API is exposed.

The pattern of using function expressions in such cases results in not being able to know what methods are exposed without going over the entire code.

Alvarez answered 20/1, 2016 at 17:43 Comment(3)
Hi, how do you call public functions from your snippet? I've tried namespace.a();Concubinage
@olivier yes, that's the idea. Although now with ES6, I usually use the shorthand syntax of object literals (ponyfoo.com/articles/es6-object-literal-features-in-depth)Dowager
I just want to make emphasis on the set of () at the end of the function definition. They are required and it's easy to miss them. I had the same issue as @Concubinage and solved it by adding them.Turbidimeter
P
2

I like Jaco Pretorius' solution, but I wanted to make the "this" keyword a bit more useful by pointing it to the module/namespace object. My version of skillet:

(function ($, undefined) {

    console.log(this);

}).call(window.myNamespace = window.myNamespace || {}, jQuery);
Pentastyle answered 2/12, 2014 at 15:39 Comment(0)
D
1

I've written another namespacing library that works a bit more like packages / units do in other languages. It allows you to create a package of JavaScript code and the reference that package from other code:

File hello.js

Package("hello", [], function() {
  function greeting() {
    alert("Hello World!");
  }
  // Expose function greeting to other packages
  Export("greeting", greeting);
});

File Example.js

Package("example", ["hello"], function(greeting) {
  // Greeting is available here
  greeting();  // Alerts: "Hello World!"
});

Only the second file needs to be included in the page. Its dependencies (file hello.js in this example) will automatically be loaded and the objects exported from those dependencies will be used to populate the arguments of the callback function.

You can find the related project in Packages JS.

Darcydarda answered 6/2, 2011 at 10:42 Comment(1)
@peter-mortensen Were these edits to my answer from '11 really necessary? It's definitely not vandalism what you are doing, don't get me wrong, but they are very superficial. I would prefer to remain the sole author of posts like these unless you really add something good.Darcydarda
A
1

If using a Makefile you can do this.

// prelude.hjs
billy = new (
    function moduleWrapper () {
    const exports = this;

// postlude.hjs
return exports;
})();

// someinternalfile.js
function bob () { console.log('hi'); }
exports.bob = bob;

// clientfile.js
billy.bob();

I prefer to use a Makefile anyway once I get to about 1000 lines because I can effectively comment out large swaths of code by removing a single line in the makefile. It makes it easy to fiddle with stuff. Also, with this technique the namespace only appears once in the prelude so it's easy to change and you don't have to keep repeating it inside the library code.

A shell script for live development in the browser when using a makefile:

while (true); do make; sleep 1; done

Add this as a make task 'go' and you can 'make go' to keep your build updated as you code.

Axilla answered 13/4, 2011 at 14:36 Comment(0)
S
1

Quite a follow-up of Ionuț G. Stan's answer, but showing the benefits of uncluttered code by using var ClassFirst = this.ClassFirst = function() {...}, which takes advantage of JavaScript's closure scoping for less namespace cluttering for classes in the same namespace.

var Namespace = new function() {
    var ClassFirst = this.ClassFirst = function() {
        this.abc = 123;
    }

    var ClassSecond = this.ClassSecond = function() {
        console.log("Cluttered way to access another class in namespace: ", new Namespace.ClassFirst().abc);
        console.log("Nicer way to access a class in same namespace: ", new ClassFirst().abc);
    }
}

var Namespace2 = new function() {
    var ClassFirst = this.ClassFirst = function() {
        this.abc = 666;
    }

    var ClassSecond = this.ClassSecond = function() {
        console.log("Cluttered way to access another class in namespace: ", new Namespace2.ClassFirst().abc);
        console.log("Nicer way to access a class in same namespace: ", new ClassFirst().abc);
    }
}

new Namespace.ClassSecond()
new Namespace2.ClassSecond()

Output:

Cluttered way to access another class in namespace: 123
Nicer way to access a class in same namespace: 123
Cluttered way to access another class in namespace: 666
Nicer way to access a class in same namespace: 666
Superlative answered 13/6, 2015 at 4:31 Comment(0)
S
1

We can use it independently in this way:

var A = A|| {};
A.B = {};

A.B = {
    itemOne: null,
    itemTwo: null,
};

A.B.itemOne = function () {
    //..
}

A.B.itemTwo = function () {
    //..
}
Saxophone answered 21/8, 2015 at 5:23 Comment(0)
H
1

In JavaScript there are no predefined methods to use namespaces. In JavaScript we have to create our own methods to define NameSpaces. Here is a procedure we follow in Oodles technologies.

Register a NameSpace Following is the function to register a name space

//Register NameSpaces Function
function registerNS(args){
 var nameSpaceParts = args.split(".");
 var root = window;

 for(var i=0; i < nameSpaceParts.length; i++)
 {
  if(typeof root[nameSpaceParts[i]] == "undefined")
   root[nameSpaceParts[i]] = new Object();

  root = root[nameSpaceParts[i]];
 }
}

To register a Namespace just call the above function with the argument as name space separated by '.' (dot). For Example Let your application name is oodles. You can make a namespace by following method

registerNS("oodles.HomeUtilities");
registerNS("oodles.GlobalUtilities");
var $OHU = oodles.HomeUtilities;
var $OGU = oodles.GlobalUtilities;

Basically it will create your NameSpaces structure like below in backend:

var oodles = {
    "HomeUtilities": {},
    "GlobalUtilities": {}
};

In the above function you have register a namespace called "oodles.HomeUtilities" and "oodles.GlobalUtilities". To call these namespaces we make an variable i.e. var $OHU and var $OGU.

These variables are nothing but an alias to Intializing the namespace. Now, Whenever you declare a function that belong to HomeUtilities you will declare it like following:

$OHU.initialization = function(){
    //Your Code Here
};

Above is the function name initialization and it is put into an namespace $OHU. and to call this function anywhere in the script files. Just use following code.

$OHU.initialization();

Similarly, with the another NameSpaces.

Hope it helps.

Heartrending answered 20/10, 2016 at 11:43 Comment(0)
S
1

JavaScript does not yet have a native representation of namespaces, but TypeScript does.

For example, you could use the following TS code (playground)

namespace Stack {
    export const hello = () => console.log('hi')
}

Stack.hello()

If you can't update your code to TS, you can at least use the pattern employed by TS when generating the JS output for namespaces, which looks like this:

var Stack;
(function (Stack) {
    Stack.hello = () => console.log('hi');
})(Stack || (Stack = {}));
Stack.hello();

Further Reading:

Semite answered 12/1, 2022 at 13:8 Comment(0)
W
0

My habit is to use function myName() as property storage, and then var myName as "method" holder...

Whether this is legitimate enough or not, beat me! I am relying on my PHP logic all the time, and things simply work. :D

function myObj() {
    this.prop1 = 1;
    this.prop2 = 2;
    this.prop3 = 'string';
}

var myObj = (
 (myObj instanceof Function !== false)
 ? Object.create({

     $props: new myObj(),
     fName1: function() { /* code..  */ },
     fName2: function() { /* code ...*/ }
 })
 : console.log('Object creation failed!')
);

if (this !== that) myObj.fName1(); else myObj.fName2();

You can also do it in a 'vice versa' way to check before object creation which is much better:

function myObj() {
    this.prop1 = 1;
    this.prop2 = 2;
    this.prop3 = 'string';
}

var myObj = (
    (typeof(myObj) !== "function" || myObj instanceof Function === false)
    ? new Boolean()
    : Object.create({
        $props: new myObj(),
        init: function () { return; },
        fName1: function() { /* code..  */ },
        fName2: function() { /* code ...*/ }
    })
);

if (myObj instanceof Boolean) {
    Object.freeze(myObj);
    console.log('myObj failed!');
    debugger;
}
else
    myObj.init();

Reference to this: JavaScript: Creating Object with Object.create()

Wherein answered 16/4, 2015 at 13:38 Comment(0)
N
0

JavaScript doesn’t support namespace by default. So if you create any element(function, method, object, variable) then it becomes global and pollute the global namespace. Let's take an example of defining two functions without any namespace,

function func1() {
    console.log("This is a first definition");

}
function func1() {
    console.log("This is a second definition");
}
func1(); // This is a second definition

It always calls the second function definition. In this case, namespace will solve the name collision problem.

Numeral answered 16/12, 2019 at 16:6 Comment(0)

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