I have an external JavaScript file that will be used on pages with lots of other scripts. My script involves a lot of jQuery that listens for events, and by design, I have many global vars declared. I've been reading best practice articles, and a lot is said about 'polluting the global namespace' and inadvertent script interaction.
What's the best way to enclose (encapsulate?) my JavaScript file so that:
I can still access some of the
variables outside of the enclosure
The jQuery event listeners will
function properly
I'm not at liberty to disclose the code, so even general responses are appreciated. Additionally, any other tips on making scripts less vulnerable to other scripts on the page are welcome.
I've found enclosure styles for regular JavaScript, but does the use of jQuery complicate this?
Generally what this boils down to is encapsulating your objects into a "namespace". I use quotes there because the term is not an official semantic in JavaScript, but rather one that is achieved through basic object encapsulation.
There are several ways to do this, and it ultimately comes down to personal preference.
One approach is to just use a basic JS object, and keep everything in it. The name of the object should be semantic and give the object some meaning, but otherwise it's purpose is to just wrap your own code and keep it out of the global namespace.
var SomeName = {
alpha: 1,
beta: {a: 1, b: 2},
gamma: function(){
SomeName.alpha += 1;
}
}
In this case, only SomeName is in the global namespace. The one downside to this approach is that everything inside the namespace is public, and you have to use the full namespace to reference an object, instead of using 'this' - e.g. in SomeName.gamma we have to use SomeName.alpha to reference the contents of alpha.
Another approach is to make your namespace a function with properties. The nice feature of this approach is you can create 'private' variable through closures. It also gives you access to closured functions and variables without full namespace referencing.
var SomeName = (function(){
var self = this;
var privateVar = 1;
var privateFunc = function() { };
this.publicVar = 2;
this.publicFunc = function(){
console.log(privateVar);
console.log(this.publicVar); // if called via SomeName.publicFunc
setTimeout(function(){
console.log(self.publicVar);
console.log(privateVar);
}, 1000);
};
}();
The other bonus of this approach is it lets you protect the global variables you want to use. For example, if you use jQuery, AND another library that creates a $ variable, you can always insure you are referencing jQuery when using $ by this approach:
var SomeName = (function($){
console.log($('div'));
})(jQuery);
One method is to namespace like this:
var MyNamespace = {
doSomething: function() {},
reactToEvent: function() {},
counter: 0
}
You will just have to refer to the functions or variable using the namespace: MyNamespace.reactToEvent. This works fine for separating what you would normally have in the window (where all the confrontation is).
You can wrap your code in an anonymous Javascript function and only return what you want to expose to the outside world. You will need to prefix var to your global variables so that they remain only in the scope of the anonymous function. Something like this:
var myStuff = (function() {
var globalVar1;
var globalVar2;
var privateVar1;
function myFunction() {
...
}
function myPrivateFunction() {
...
}
return {
var1: globalVar1,
var2: globalVar2,
myFunction: myFunction
};
})();
Now you can access myStuff.var1 and myStuff.myFunction().
Two ways to encapsulate or limit namespace pollution
1) Create one global var and stuff everything you need into it.
var g = {};
g.somevar = "val";
g.someothervar = "val2";
g.method1 = function()
{
// muck with somevar
g.somevar = "something else";
};
2) For inline scripts, consider limiting the scope of the functions called.
<script>
(
function(window)
{
// do stuff with g.somevar
if(g.somevar=="secret base")
g.docrazystuff();
}
)(); // call function(window) then allow function(window) to be GC'd as it's out of scope now
</script>
I just started using RequireJS and have now become obsessed with it.
It's basically a dependency management system in a modular JavaScript format. By doing so you can virtually eliminate attaching anything to the global namespace.
What's nice is that you only reference one script on your page require.js then tell it what script to run first. From there it is all magic...
Here's an example implementation script:
require([
//dependencies
'lib/jquery-1.6.1'
], function($) {
//You'll get access to jQuery locally rather than globally via $
});
Read through the RequireJS API and see if this is right for you. I'm writing all my scripts like this now. It's great because at the top of each script you know exactly what you dependencies are similar to server-side languages - Java or C#.
This is a common practice with jQuery plugins for the same reasons you mention:
;(function ($) {
/* ... your code comes here ... */
})(jQuery);
This is an immediate function. If you declare your "global" variables inside, they will be local to this closure (still "global" for the code you create inside). Your event listeners will work inside here too, and you will still be able to reach real global variables.
Related
I'm not sure which JavaScript design pattern I'm following. Can someone please help shed some light on it?
var masonrySupport = ({
large__videos__support: function() {
$('.masonry-container .largeRec').find('.itemMasVideo').parent().addClass('item_largeRec_video_height');
},
smallRec__videos__support: function() {
$('.masonry-container .smallRec').find('.itemMasVideo').parent().addClass('item_smallRec_video_height');
},
init: function() {
this.large__videos__support(),
this.smallRec__videos__support()
}
})
masonrySupport.init();
There are two "patterns" I can see here.
Using self invoking closure to isolate scope.
(function($) {
// Code here
})(jQuery);
Helps mitigate the creation of accidental global variables.
(Kind) the module pattern, where you create an object with a bunch of methods on it, and call init(). I prefer to self invoking closure version of it. The Revealing Module Pattern.
The pattern you are using is called the Module Pattern, and it is one of the most important patterns in JavaScript. You outer wrapper creates an anonymous scope that provides privacy and state to the code that you place inside it.
(function($) {
// Everything in here is private and stateful
// and we can access jQuery through the imported $ variable
})(jQuery);
To your scope, you're also passing the global jQuery object. This method is called global import, and is faster and clearer than accessing the implied global from within your scope.
Inside your scope, you are creating an API that is accessible through the masonrySupport variable, making it a Revealing Module Pattern.
I don't see this as a design pattern in the strict sense of terminology. May be associated with the module pattern, but it needs to return something to be accessible outside of it's inner scope. It's only a self executing function invoked inside a scope which in this case is jQuery. This is used in many jquery plugins. You isolate the scope of the self executing function to a specific - lets say - domain.
This can be found on the first declaration:
(function($) {
...
})(jQuery);
By closuring the function you are guarding the functions and variables declared inside the scope to a specific domain, in this way eliminating the possibility to accidentally override or redeclare some function or variable declared in the global scope. It's a common practice to isolate the scope from the global object which in Javascript world is the Object or on DOM context is window.
And it continues with the self executing function:
$(function() {
...
})
Effectively what is being done here is, once the document loads, execute two functions - 'large__videos__support' and 'smallRec__videos__support.'
Let's understand how it is being achieved,
Firstly it is Immediately-Invoked Function Expression (IIFE) in action. This pattern is often used when trying to avoid polluting the global namespace, because all the variables used in the function are not visible outside its scope.
(function($) {
...
})(jQuery);
Short hand of $( document ).ready() is being used. More here.
$(function() {
...
});
Thirdly, you are initializing one object being referenced by 'masonrySupport' and calling its method 'init.'
In JS, this is called and Immediately Invoked Function Expression (IIFE), and is known as the module pattern.
However in jQuery this pattern is used to create jQuery Plugins. I advise you to follow the best practices to make it work.
Check that jsfiddle to get you started.
Below the JS part:
(function( $ ) {
$.fn.masonrySupport = function( option ) {
if ( option === "large") {
this.find('div.itemMasVideo').parent().addClass('item_largeRec_video_height');
}
if ( option === "small" ) {
this.find('div.itemMasVideo').parent().addClass('item_smallRec_video_height');
}
return this;
};
}( jQuery ));
$( 'div.masonry-container.largeRec' ).masonrySupport( "large" );
Im designing an API that requires my users to download a javascript file from my server and then load it on their pages. Inside this file there is a function call generic(), if my users include this js and for some reason they have a piece of js on their page where there is another function call generic() this will represent an issue. Im not a front end dev, I know that with php you can solve this creating a class and putting all your functions inside, so you can call them like $myclass->myfunction();, but how can i solve this on js? Is this even a good approach on js? (no jquery please.)
You will obviously always have to expose at least one identifier globally, but a common approach is to wrap everything in an immediately-invoked function expression:
var YourNamespace = (function () {
var privateData = 10; // Not accessible outside the IIFE
// Expose public properties (these functions can access the private data)
return {
someMethod: function () {
// Do stuff
},
anotherMethod: function () {
// More stuff
}
};
}());
This will expose a single identifier, YourNamespace, as an object with properties that can be used as methods. You can use it like this:
YourNamespace.someMethod();
Wrap your code inside a wrapper object/ or function.
var MyLibrary = {
global1: 123,
global2: 'abc',
doSomething: function(a){
// ...
},
somethingElse: function(b){}
};
If u are looking for Encapsulation in Javascript, then u are looking for Closures
I am not a really good JavaScript user but I can get things done with it. I am not proud of the code I have written in JavaScript, so I decided to change that. Here is my first step:
I am trying create my own library for a project and the below is the initial structure.
window.fooLib = {};
(function (foo) {
"use strict";
foo.doSomeStuff = function(param1) {
console.log(new AccommProperty(param1));
}
//some internal function
function AccommProperty(nameValue) {
var _self = this;
_self.name = nameValue;
}
}(fooLib));
I used immediately invoked function expression here to initialize my variable. In this case it is fooLib.
I am not sure if I should do some other things to make window.fooLib more safe. I mean it can be overridden by any other code which will run after my code if I understand JavaScript correctly.
What are your thoughts?
If you want to prevent overwriting your variables, you may use Object.defineProperty() with writable:false, configurable:false. In your case:
(function () {
"use strict";
var foo = {};
//some internal function
function AccommProperty(nameValue) {
var _self = this;
_self.name = nameValue;
}
foo.doSomeStuff = function(param1) {
console.log(new AccommProperty(param1));
}
Object.defineProperty(window, "foolib", {value:foo});
}());
Still, there is no good reason for that. It would need EcamScript 5.1 to work, and there are no shims around; maybe something with getters/setters to prevent overwriting with the = operator.
But also, there should be no need to make your library un-overwritable. Just don't use code on your site that overrides the lib. Or maybe someone even wants to overwrite your functions with another, better lib with the same interface?
If the question is about a library to be shared, with possible namespace conflicts to others, you may have a look at jQuery.noConflict.
Every JavaScript object can be overriden. This is the nature of JavaScript and it is impossible to change it. So you cannot make your code safe in that sense.
As for selfinvoked functions: you should use them when you want to have local variables but viisible to all your functions. So in your case AccommProperty is such variable. Defining doSomeStuff inside scope makes no difference unless doSomeStuff will use variables defined inside scope.
So when you want to hide variables from user and/or you need globals and you are affraid of name conflicts use selfinvoked functions.
I am not sure if I should do some other things to make window.fooLib more safe. I mean it can be overridden by any other code which will run after my code if I understand JavaScript correctly.
You could try making window.fooLib a local variable instead. Using closures and nested functions one can emulate a namespace where you can put all your data instead of putting it into the global scope or attaching it to window object:
(function() {
// all functions nested in foo() have access to fooLib.
fooLib = {}
fooLib.doSomeStuff = function(param1) {
console.log(param1);
console.log(fooLib);
}
//some internal function
function AccommProperty() {
console.log(fooLib);
}
}());
See Javascript Closures: Encapsulating Related Functionality for more details.
Long story short, I have a long code that uses jQuery. Lots of files, functions, etc. A less than ideal amount of our users are having issues with our code because some addons, toolbars and the like they have installed breaks our JavaScript code because of jQuery gets included twice and nasty stuff like that.
I thought I could just
Include jQuery
Use $.noConflict
Then include the whole rest of my code between something like:
.
(function($) {
// All of my code goes here.
})(jQuery);
I haven't checked if this fixes our issues with those users, but it does work. The problem is, in one part of the site (image upload) we have an iframe that needs to call some of those functions defined in our big chunk of code. I've tried putting those functions out of this unnamed function call, but it uses, on itself, other functions which have to be there.
Any idea or workaround of how could I be able to access functions defined inside that function (shown above) from a code that's outside of it?
Thanks!
You cannot access a function context from the "outside world". Well, to be accorate you could do it in some older js engines which allowed for accessing .__parent__ attributes, but that is old'n'busted and no longer available.
However, you would need to either expose some functions within your closure, or you creating a namespace object where you write all of your logic in (which also has to be available in the parent context).
So I'd suggest something like
(function( $ ) {
function myFunc() {
// do stuff
}
function anotherFunc() {
}
window.myFunc = myFunc; // expose myFunc globally
}( jQuery ));
Maybe even better:
var myNameSpace = { };
(function( $ ) {
myNameSpace.myFunc = function() {
// do stuff
};
}( jQuery ));
// somewhere else
myNameSpace.myFunc();
It is not an ideal practice, but you can declare those functions in the global scope.
(function($) {
globalFunct = function (arg1, arg2) { // Don't use var keyword
...
};
})(jQuery);
It isn't ideal because you can run into naming collisions, much like you are observing with jQuery. Improve upon this approach by putting all of your globally-accessible methods in a "package." Choose a unique name for it. This will prevent collisions.
// Somewhere outside of your anonymous function, in the global scope
var myPackage = {};
(function($) {
myPackage.globalFunct = function (arg1, arg2) {
...
};
})(jQuery);
Then call that method by invoking myPackage.globalFunct().
Why are you wrapping your code in a call to the jQuery function object which you pass in to your self-executing anonymous function; are you meaning to create a jQuery object from all of your code?
In order to expose your code to the outside world, you need to assign your functions and objects to an object which is outside of the scope of your code, such as the window object.
For example, if you had created an object containing various methods and properties that you wanted to expose, you could do this:
//Your self-executing anonymous function
(function($)
{
//Object which contains various useful methods and properties
var useful = {...};
//Expose it to the outside world
window.Useful = useful;
})(jQuery);
EDIT: as others have noted, it is not an ideal solution as you will indeed run into naming collisions if you are not careful. Also, using an object external to your anonymous function as a namespacing object (as others have stated) is my preferred method
Yes, you can "export" the function from within a closure:
Yes, you can "export" the function from within a closure:
(function() {
function a() {
console.log("a");
}
function b() {
a();
console.log("b");
}
// make b globally available
window.b = b;
})();
b();
window.PARTY_CATS_jQuery = jQuery.noConflict(true);
(function($) {
$(function() {
// All of my code goes here.
});
})(COMPANY_NAME_jQuery);
Then just use PARTY_CATS_jQuery in your global functions
If you feel PARTY_CATS_ is not a unique enough name pick something safer like BABY_KILLER_jQuery
So I'm a fairly decent javascript programmer and I've just recently finished working on a fairly big web application that involved writing quite a bit of javascript. One of the things I can across when I was debugging my script was that there were some namespace conflicts with my various global variables I used throughout my script. Essentially, my javascript file was structured as such:
global var a
global var b
global var c
function1(){}
function2(){}
function3(){}
with a jQuery document on-ready function to bind various events to buttons in my html and call my functions as event handler callbacks.
Some people recommended encapsulating my entire script in one gigantic function to prevent any scope-related errors. I couldn't quite figure out exactly what that would entail. Any tips are appreciated as I am about to create another web app that will involve quite a bit of AJAX page loads to avoid browser refreshes and DOM manipulation bound to various events. Thanks!
I recommend reading the jQuery plugin authoring guide (I also recommend you consider using jQuery if you are not)
http://docs.jquery.com/Plugins/Authoring
BTW this been asked many times (not a criticism for re-asking)
jQuery: Global Variable Namespace Problem
Avoiding polluting the global namespace with javascript dependencies
JavaScript Namespace
I also highly recommend you read about jQuery live plugin for register DOM events(I guess its built-in now):
http://api.jquery.com/live/
(this will minimize the nasty need for state management of unbinding and rebinding your DOM nodes).
A similar alternative to Michael's and nnnnnn's version is to do
var YourApp = {
a: 1234,
b: 5678,
function1: function () {
},
etc
};
YourApp is the only global var and its properties can be accessed like
YourApp.function1();
or
YourApp.a;
I like wrapping the contents of each file inside an anonymous function. You can then pass window to this as a parameter and selectively choose what to export from each file.
(function(exports) {
var MyClass = function() {
};
MyClass.prototype.method = function() {
};
// this won't be visible outside this file
var helperFunction = function() {
};
exports.module = exports.module || {};
exports.module.MyClass = MyClass;
})(window);
Also, you can structure it in the following way to use this as the global object instead, if that appeals more to your coding style:
(function() {
this.Thing = function() { };
}).call(window);
I expect to get downvoted from OO purists, but...
A very simple solution to the namespace collisions is to place your variables and functions into a class, even if it doesn't have a working constructor or perform any internal processing of its own.
function YourApp() {} // empty constructor...
YourApp.a = 1234;
YourApp.b = 5678;
YourApp.function1 = function() {};
YourApp.function2 = function() {};
function YourOtherApp() {} // empty constructor...
YourOtherApp.a = 1234;
YourOtherApp.b = 5678;
YourOtherApp.function1 = function() {};
YourOtherApp.function2 = function() {};
// Then you call it like:
YourApp.function1();
// And you have no more namespace collisions with other globals
The quickest first step based on what you have done in the past with lots of global variables and functions is to simply take all of those and make them properties of a single object. That single object is declared as a global variable, but it is your only global variable and is effectively your new namespace and thus you only have to worry about one name potentially clashing with other libraries.
So relating that directly to the example you gave with a, b, etc:
var SNS = {}; // create some namespace object
SNS.a = "something";
SNS.b = "something else";
SNS.c = 17;
SNS.method1 = function(x) {
alert(SNS.a + x);
};
SNS.method2 = function() {
SSN.method1(12); // call another function
};
SNS.SUB = {};
SNS.SUB.property1 = "sub namespace prop 1";
SNS.SUB.method1 = function() {};
// etc.
My example uses 'SNS' for 'some namespace'; I'm sure you can immediately see how that would be pretty easy to apply to the project you just finished. You can probably also see the disadvantage that for your methods to refer to each other and to your variables you have to prefix them all with the name of your object. If you have sub namespaces that gets worse. Fortunately there are ways around that, but I'm declaring them outside the scope of this answer.
Having said all that, something for you to read up on (Google) is the "revealing module pattern" - will help you go a bit more OO (if that's what you want).
A really in-depth answer to your question can be found here: http://enterprisejquery.com/2010/10/how-good-c-habits-can-encourage-bad-javascript-habits-part-1/
Further reading:
http://www.adequatelygood.com/2010/3/JavaScript-Module-Pattern-In-Depth