I've been seeing a number of people wrapping their controllers with:
function(){
//CODE
}();
What's the benefit / goal there?
That isn't really anything related directly to Angular, it is a JS pattern know as an Immediately Invoked Function Expression.
It is one of the most useful patterns in JavaScript, primarily because of:
Code Encapsulation
Since functions have closures in JS, we can use this pattern to create private data very easily:
var index = (function iife() {
var counter = 0; // <-- this is private, only available inside the closure of inner()
return function inner() {
return counter++;
};
})();
console.log(index()); // 0
console.log(index()); // 1
console.log(index()); // 2
console.log(index.counter) // undefined
We can also pass arguments into an IIFE, which allows us to control how we access the outside context of our IIFE. For example, to make sure $ is actually the jQuery object within your code:
(function ($) {
// here have access to the global jQuery as $ regardless of what window.$ is and
// how many libraries are trying to use $
})(jQuery);
By combining the two ideas above, IIFEs can also be used to implement the module pattern, which is the basis for how RequireJS and NodeJS separate code:
var myModule = (function iife(initData) {
// we can use initData here to initialize our module if necessary
var module = {};
// private vars ...
var privateVar1, privateVar2;
// private methods ...
function privateMethod() {
console.log('yeeey');
}
module.somePublicProperty = 1;
module.somePublicMethod = function() {
privateMethod();
};
return module;
})(/* pass initialization data */);
myModule.somePublicMethod(); // 'yeeey'
The reason you'll find a lot of JavaScript code wrapped in an anonymous function is to isolate it from other code on the page.
The following code will declare a variable called name on a global scope:
var name = "Hello World";
By using that code, any other script on the page attempting to use a variable called name could potentially get an unexpected value of "Hello World" because your script declared it as "Hello World".
By wrapping that code in an anonymous function, you keep the code from conflicting with other variables called name:
(function() {
var name = "Hello World";
})();
In the example above, name is now only available inside of the scope of the anonymous function. It is not global, and therefore cannot conflict with other code on the page.
By wrapping your Angular module in an anonymous function, you prevent your code from conflicting with other code.
Additionally, other people who may use your code won't have to worry about it changing their global scope.
IMHO it's not necessary, even superfluous, as most controllers are already functions:
'use strict';
angular.module('MyApp').controller('AboutController', ['$scope'
function ($scope) {
$scope.title = 'About Us';
}
]);
Everything #nem035 and #tcasey said is correct but it also have another side effect.
If you use tools like Grunt or Gulp it also allow you to have working dists to put in production.
If you do not use Immediate Invoke Pattern you'll most likely have minification problems like:
State X is already defined!
Unknown provider
. . .
I suggest you to wrap all your js modules with this pattern.
I hope I've been helpful.
There are many benefits of you immediately-invoked-function-expression short IIFE and it's best practice to use it. This way each of angular service or controller become isolate and you don't run into global variables as it can happened if you don't use IIFE.
read more about it
Related
I'm just getting started with javascript modules and I want to make sure I'm doing it correctly.
Below is an example of the methodology I'm following, based on the "Loose Augmentation Pattern" that I read about here
//myApp.js
var myApp = {};
//someModule1.js
(function (ma) {
ma.someModule1.DoStuff = function () {
alert("hi");
};
return ma;
}(myApp || {}));
//someModule2.js
(function (ma) {
ma.someModule2.DoMoreStuff = function () {
alert("ho");
};
return ma;
}(myApp || {}));
//someModule3.js
myApp.someModule1.DoStuff();
myApp.someModule2.DoMoreStuff();
The myApp variable within myApp.js would be the only variable that's globally exposed, with all of the other modules and their functions only being accessible via this variable.
someModule3.js isn't necessarily a module, but any arbitrary javascript wanting to access the properties of the myApp object (After the appropriate modules have been defined).
The part in particular I'm not 100% clear on is this: (myApp || {}, jQuery)
What is that part called and what exactly is it doing (I know the whole thing is a closure, but I just don't understand exactly how the last part is working)?
It seems like "ma" is initially nothing, I add a function to it in the body of the closure, then return ma. At this point myApp only has the one function.
In the bit at the end (myApp || {}), is it actually saying "ma isn't nothing, it's actually called myApp and I'll append those functions to that object if it exists."
Is that right or am I way off?
I see four issues:
Your code won't run as is. You have to define .someModule1 before you can assign to it.
There's no reason to do return ma because you aren't using the return value.
There's no reason to pass myApp || {} because if myApp is not defined, then your code will do nothing because the object you created would not be capture in any variable and will just be immediately garbage collected and not be accessible.
As you've shown your code, the IIFE you've enclosed the code in is not accomplishing anything other than adding lines of code and complexity.
Here's more detail on each issue.
Your modules won't run as is. You need to define .someModule1 by changing this and there is no reason in your code to pass myApp || {}:
//someModule1.js
(function (ma) {
ma.someModule1.DoStuff = function () {
alert("hi");
};
return ma;
}(myApp || {}));
to this:
//someModule1.js
(function (ma) {
// you must define .someModule1 before you can assign properties to it
ma.someModule1 = {};
ma.someModule1.DoStuff = function () {
alert("hi");
};
return ma;
}(myApp));
There is also no reason to do return ma in your code since you are not using the return value.
The reason myApp || {} is of no value here is because if myApp is not defined, then none of the code in your module does anything useful because the underlying object you would be assigning things to is not captured in a variable anywhere. So, if myApp is not defined, then your code accomplishes nothing. So, somewhat by definitino, myApp has to already be defined for your code to be useful, therefore, you can just pass myApp into the IIFE.
As you've shown the code, there is no benefit or reason to putting the assignment of properties inside the IIFE. You don't have any closure variables or anything that is private inside the IIFE. So, you would achieve exactly the same result with this:
myApp.someModule1 = {};
myApp.someModule1.DoStuff = function () {
alert("hi");
};
There are some reasons for using an IIFE, but you don't show any in this code example. Personally I'm a fan of using the simplest code that achieves your objectives and not adding extra complexity just for sake of it. Other people like to put all their code inside these IIFE modules. I only put my code inside an IIFE when there is actually a reason to have your code in an IIFE.
I've been using a pattern in my node.js modules that seems so obvious to me that I assume there must be something wrong with it or I would see more people doing it. To keep private variables that are global to the module, I simply attach them as properties on the module object. Like so:
module.exports = {
init: function() {
module.someClient = initializeSomethingHere()
},
someMethod: function(done) {
module.someClient.doSomething(done)
}
}
This seems preferable to me than something like this...
var someClient;
module.exports = {
init: function() {
someClient = initializeSomethingHere()
},
someMethod: function(done) {
someClient.doSomething(done)
}
}
...because in the second example you need to go searching for var someClient at the top of the file to make sure that the omission of the var keyword is intentional within the init method. I've never seen this pattern used elsewhere though, so I wonder if I'm missing something that makes it less than ideal.
Thoughts?
There are a couple of possible downsides that come to mind.
1) It's technically possible for those properties to be accessed and modified outside the module, but only if a reference to the module itself is available outside it. Something that makes the module available through its own exports (module.exports = module; being the simplest example) would expose them.
2) You could have a naming conflict with a builtin property or a future builtin property that doesn't exist yet (which would cause your code to break in future versions of node.js). This could be very problematic and very hard to debug. Currently the built-in properties on a module object are: children, exports, filename, id, loaded, paths, and parent.
because in the second example you need to go searching for var someClient at the top of the file to make sure that the omission of the var keyword is intentional within the init method.
If that is the reason, you could just use a namespace that isn't module. For instance by adding var private = {}; to the top of each file and then using private.someClient instead of module.someClient.
Also 'use strict'; so that the accidental omission of var is an error and not an accidental global.
Drawbacks
Option 1: This practice is prone to naming conflict with a builtin property or a future builtin property that doesn't exist yet, as #paulpro stated in his answer.
Option 2: If you miss var keyword and expose the someClient globally. Besides you need to go searching for var someClient at the top of the file all the time.
Alternative
As JavaScript has function scope it's better to define everything within a function. Creating private and public members within a function. Below is a design pattern which one can follow:
'use strict';
module.exports = (function(){
//private
var someClient;
//public properties
var that={};
that.init = function() {
someClient = initializeSomethingHere()
},
that.someMethod: function(done) {
someClient.doSomething(done)
}
//expose only the required methods
return that;
})();
Here only exposed methods are those which are attached to that object. And all rest are private to the function scope. Even if you miss the var keyword in someClient it won't be accessible out side of the function, which won't ever happen if you use 'use strict' at the top.
Logic is first time when you require the xyz.js file it will return the that object rather than the function.
I need a few global variables that I need in all .js files.
For example, consider the following 4 files:
global.js
js1.js
js2.js
js3.js
Is there a way that I can declare 3 global variables in global.js and access them in any of the other 3 .js files considering I load all the above 4 files into a HTML document?
Can someone please tell me if this is possible or is there a work around to achieve this?
Just define your variables in global.js outside a function scope:
// global.js
var global1 = "I'm a global!";
var global2 = "So am I!";
// other js-file
function testGlobal () {
alert(global1);
}
To make sure that this works you have to include/link to global.js before you try to access any variables defined in that file:
<html>
<head>
<!-- Include global.js first -->
<script src="/YOUR_PATH/global.js" type="text/javascript"></script>
<!-- Now we can reference variables, objects, functions etc.
defined in global.js -->
<script src="/YOUR_PATH/otherJsFile.js" type="text/javascript"></script>
</head>
[...]
</html>
You could, of course, link in the script tags just before the closing <body>-tag if you do not want the load of js-files to interrupt the initial page load.
The recommended approach is:
window.greeting = "Hello World!"
You can then access it within any function:
function foo() {
alert(greeting); // Hello World!
alert(window["greeting"]); // Hello World!
alert(window.greeting); // Hello World! (recommended)
}
This approach is preferred for two reasons.
The intent is explicit. The use of the var keyword can easily lead to declaring global vars that were intended to be local or vice versa. This sort of variable scoping is a point of confusion for a lot of Javascript developers. So as a general rule, I make sure all variable declarations are preceded with the keyword var or the prefix window.
You standardize this syntax for reading the variables this way as well which means that a locally scoped var doesn't clobber the global var or vice versa. For example what happens here is ambiguous:
greeting = "Aloha";
function foo() {
greeting = "Hello"; // overrides global!
}
function bar(greeting) {
alert(greeting);
}
foo();
bar("Howdy"); // does it alert "Hello" or "Howdy" ?
However, this is much cleaner and less error prone (you don't really need to remember all the variable scoping rules):
function foo() {
window.greeting = "Hello";
}
function bar(greeting) {
alert(greeting);
}
foo();
bar("Howdy"); // alerts "Howdy"
Have you tried it?
If you do:
var HI = 'Hello World';
In global.js. And then do:
alert(HI);
In js1.js it will alert it fine. You just have to include global.js prior to the rest in the HTML document.
The only catch is that you have to declare it in the window's scope (not inside any functions).
You could just nix the var part and create them that way, but it's not good practice.
As mentioned above, there are issues with using the top-most scope in your script file. Here is another issue: The script file might be run from a context that is not the global context in some run-time environment.
It has been proposed to assign the global to window directly. But that is also run-time dependent and does not work in Node etc. It goes to show that portable global variable management needs some careful consideration and extra effort. Maybe they will fix it in future ECMS versions!
For now, I would recommend something like this to support proper global management for all run-time environments:
/**
* Exports the given object into the global context.
*/
var exportGlobal = function(name, object) {
if (typeof(global) !== "undefined") {
// Node.js
global[name] = object;
}
else if (typeof(window) !== "undefined") {
// JS with GUI (usually browser)
window[name] = object;
}
else {
throw new Error("Unkown run-time environment. Currently only browsers and Node.js are supported.");
}
};
// export exportGlobal itself
exportGlobal("exportGlobal", exportGlobal);
// create a new global namespace
exportGlobal("someothernamespace", {});
It's a bit more typing, but it makes your global variable management future-proof.
Disclaimer: Part of this idea came to me when looking at previous versions of stacktrace.js.
I reckon, one can also use Webpack or other tools to get more reliable and less hackish detection of the run-time environment.
Yes you can access them. You should declare them in 'public space' (outside any functions) as:
var globalvar1 = 'value';
You can access them later on, also in other files.
I have defined the following piece of Coffeescript code below, which defines a function using RequireJS:
define 'PersonService', ['jquery'] ($) ->
getPerson = (id) ->
person = dataService.GetPerson id
{ getPerson: getPerson}
It produces the following:
(function() {
define('PersonService', ['jquery'](function($) {
var getPerson;
getPerson = function(id) {
var person;
return person = dataService.GetPerson(id);
};
return {
getPerson: getPerson
};
}));
}).call(this);
I guess the issue I have is with the self-executing function that is produced from the Coffeescript code. Will this cause issues that I am possibly not tracking? Or is this proper.
Thank you.
It's correct
The difference between not having a wrapped function and having one is to do with scope.
If you define var a = 10; in the global scope a becomes global with or without the var keyword.
When wrapped all variables are local to the wrapped function so do not end up global.
In you example everything is already wrapped in a function so yes you don't need the extra wrapping!
You can tell coffee-script not to add the wrapper function using
coffee -b, --bare compile without a top-level function wrapper
IMHO: It's better to always have the wrapper function so you don't need to think about it on a file to file basis.
I'm working on a proprietary site, and I'm having some issues. I'm using jQuery along with prototype, and I've got it namespaced properly, so in this question assume you can use $ or jQ as a namespaced reference to jQuery.
So I've got a bunch of functions, some mix jQuery and javascript, some plain javascript, some jQuery only. Now, currently some functions are defined within the document.ready jQuery function, and some are defined outside of it, kind of like this:
jQ(document.ready(function($) {
if ( ifConfig ) {
//page check, function calls here
fnc1();
fnc2();
fnc3();
fnc4();
}
function fnc1() {
//fnc code in here
}
function fnc2() {
//fnc code in here
}
}); //end document.ready
function fnc3() {
}
function fnc4() {
}
Now this is all pseudo code, you can assume the functions are valid and have valid code in them. Recently I was doing some debugging, and one of my functions that was declared and called inside the document.ready said it was undefined. I moved it outside of the document.ready, and everything worked again.
I'm basically trying to understand the order of how functions are initiated/called better, so my question is when do you declare functions inside the document.ready and when do you declare them outside? Do you only declare inside when they're called within that document.ready only? Or should I always just declare them outside of that document.ready?
Thanks.
Generally, you should declare & define your own namespace, where all of your application logic (including functions/methods) is located. That way you avoid collision with other scripts on your site + that way your code is much cleaner and easier to maintenaine.
var myapp = function(){
var foobar1 = null,
foobar2 = null,
foobar3 = null;
return {
getFoobar1: function(){
return foobar1;
},
getFoobar2: function(){
return foobar2;
},
setFoobar1: function(foo){
foobar1 = foo;
},
clickhandler: function(e){
alert('I am an event handler, and I am not anonymous');
}
// etc.
};
};
$(document).ready(function(){
var Application = myapp();
Application.getFoobar2();
$(document).bind('click', Application.clickhandler);
});
That pattern (some call it the "method pattern") creates a closured function/object which also guarantees private member variables within your namespace, only accessible through the getter functions from the outside.
This is really only a pretty basic example, you can push this idea & pattern to an extend, which is very nice & a good thing (IMO).
A great book about this stuff which was named and recommended pretty often is "Javascript: The Good Parts" by Douglas Crockford.
If a function is only used inside the document ready function, then declare it inside so you don't pollute the global scope. Otherwise, declare it outside so it the rest of your script has access to those functions.
(document).ready is more used for things that need to be executed at page load, and not function declarations. If you declare them inside of (document).ready, their scope will be local to that block - if they're only used locally, that's fine and they should be declared there. Otherwise, declare them outside.
So in your example, if the functions are only used in that block, they should be declared in there. If they're used other places additionally, they should be declared outside.