This question already has answers here:
What is the (function() { } )() construct in JavaScript?
(28 answers)
Closed 6 years ago.
I have seen various code which is implemented in following two way. I always use the second one (2.). I wanted to know two thing here.
Is there any difference between these two codes?
Which one is the best practice (and why) if any?
1.
(function () {
//some code here, angular code
})();
2.
(function () {
//some code here, angular code
});
Please also suggest me some good blog or book in this regards as I wants to learn in more detail. Thank you all advance..
Yes, you are not executing the second one.
In the first example, you are declaring an anonymous function, which gets run afterwards with no parameters.
In the second example, you are just declaring it, but not running it.
() is what makes it run, in this case by passing it no parameters.
This one executes the anonymous function:
(function () {
//some code here, angular code
})();
This one doesn't execute it:
(function () {
//some code here, angular code
});
For example, if you have a parameter, you can pass it like so:
(function (c) {
// c.log() is same as console.log
c.log("hello");
})(console);
Note: I've added the parameter example because it's less obvious without any parameter.
Edit:
As #Osman has just pointed in the comments, the first one is known as IIFE.
This pattern is so common, a few years ago the community agreed on a
term for it: IIFE, which stands for Immediately Invoked Function
Expression.
The second is declaration, the first is declaration and execution.
Difference:
The first one executes the anonymous function expression:
(function () {
//some code here, angular code
})();
The second one doesn't execute it:
(function () {
//some code here, angular code
});
anonymous function is a function that doesn't have a name.
Background:
Basically, first we are wrapping the anonymous function declaration with first brackets, like: (), to make it a function expression:
// this is a function declaration:
function () {
//some code here
}
// this is a function expression
(function () {
//some code here
});
By itself it does nothing, as we are neither executing it, nor declaring it within the current scope. In other words, it's useless. Learn more about the difference between function declaration & function expression.
Now, we can use the function expression as a parameter to some other function, like jQuery does:
// now jQuery is taking the function expression as parameter
$(function () {
//some code here
});
Or, we can execute the function itself by using () at the end (This is how we invoke any function actually - in this case without any parameter):
// Now the function expression gets executed.
(function () {
//some code here, angular code
})();
This is also known as Immediately-Invoked Function Expression or IIFE.
The above examples don't have any parameter. However, if you have a parameter, you can pass it like so while executing:
(function (c) {
// Here c.log() is same as console.log()
c.log("hello");
})(console);
Note: I've added the parameter example because it may be less obvious without any parameter.
Best Practice:
Since functionally they are different, the question of best practice doesn't appear. Usually we use IIFE in cases where we want to execute something in a scope different from the current scope & we don't want to leave any footprint of function declaration, variable declaration etc. within the current scope.
Further Reading:
More discussion about this can be found in the following links:
What is the (function() { } )() construct in JavaScript?
What is the purpose of wrapping whole Javascript files in anonymous functions like “(function(){ … })()”?
What is the purpose of a self executing function in javascript?
You Don't Know JS: Scope & Closures.
The first one is an IIFE (Immediately-invoked function expression ) as others said, for more info on IIFE check this repo by Kyle Simpson (author of You don't know JS)
Related
What are the difference among -
First :-
(function () {
var Book = 'hello';
}());
Second:-
(function () {
var Book = 'hello';
})();
First and second are similar some how in work..
Third :-
(function ($) {
var Book = 'hello';
})(jQuery);
What pattern I need to use and where in my coding.. Third module pattern I have seen while I was reading a article related to backboneJS.
What I understood from Third one "self executing function with the argument “jQuery”" ....
Can any please give me some idea about Immediately Invoked Function Expressions (IIFE).
Thanks !!
In all cases you are doing an anonymous function. I think 1 is the same as 2.
In the third case you are passing jQuery as an argument. This is done when you want to encapsulate jQuery within your function's scope.
For instance, in your application, jQuery var could be jQuery. But within your anonymous function you may want to use it as $.
(function ($) {
//Here jQuery is $
var Book = $(document.body).text();
})(jQuery);
//Out of your function, you user jQuery as jQuery (in this example)
var Book = jQuery(document.body).text();
This is called a closure to avoid conflicts with other libraries such as mootools which are using $. This way you can ensure to use $ in that function with passing jQuery as a param.
(function ($) {
$(function () { // Here in this block you can use '$' in place of jQuery
.......
});
})(jQuery); //<----passing jquery to avoid any conflict with other libraries.
Immediately-invoked function expressions (IIFE) is one of the core JavaScript features. Its main aim is not to clutter the namespaces with disposable functions and variables.
if you use a variable or a function only once, you don't need to make it available for the rest of the code (therefore you make a private access, for example). In case of functions, you may just let them be anonymous, just like the following:
(function(){
console.log("Hello symfony world!");
}());
Please check with this link
Furthermore here is a useful explanatory video in less than 7 minutes
As the other answers pointed out they are all self executing anonymous function or immediate anonymous functions.
The third example is use to create aliases for variables outside the function. This is a good way to prevent name conflicts and creating code where it's possible to easily change a module used in the function. It's essentially a form of dependency injection.
(function (doc, win, $, myModule) {
// Code
}(document, window, jQuery, window.MYAPP.myModule));
doc, win, $ and myModule are injected variables. With this pattern it's trivial to change any of the injected components. Like this
(function (doc, win, $, myModule) {
// Code
}(document, window, jQuery, window.MYAPP.myModule2)); //Use myModule2 instead myModule
Like every other answer has said, in the third function you are passing JQuery to the function.
I would like to take a moment and explain why the first two are the same.
When you create a function, the name of that function is really a function pointer. For instance, in function foo(){}, foo is a pointer to the function that you just made (which explains stuff like this). You dereference that pointer (and thus execute the function) by adding parenthesis at the end of the function name: foo().
So if we look at that code again, in number one, first you create the function:
function () {
var Book = 'hello';
}
And then you dereference it, effectively executing the function: ()
In the second example, you surround the entirety of the function creation in parenthesis:
(function () {
var Book = 'hello';
})
This ensures that you perform the creation operation before your next command, which is to dereference the function again: (). The parenthesis in this case are not really necessary, as the function will be created before it is executed anyway.
All three examples are Immediately Invoked Function Expressions (IIFE).
The only difference is that in the third example jQuery is being passed in as a variable allowing you to use it within the IIFE using its dollar naming convention. e.g.
(function ($) {
var Book = 'hello';
$('#bookelement').html(Book);
})(jQuery);
These all are self executing functions. Now days also known as Immediately Invoked Function Expressions (IIFE).
First two are exactly same with slightly different syntax and third is passing a parameter as jQuery object.
In fact, all three are self executing function's and ti really depends on what you are needing to do.
The only difference between is between 3. 1 and 2 are the same.
The difference with 3 is that you are passing a reference to jquery as an argument. Now all functions inside this annoyomus function have access to jque
All of these are example of self invoking function.
This will give you a clear view:-
var my_func = function(){
var internal_var = "Hello";
return internal_var;
};
var my_func2 = function(name){
var internal_var = "Hello";
return internal_var;
};
var long_var_name = "I can be some object or number or object or array";
var result1 = (my_func());
var result2 = (my_func)();
var result3 = (my_func2)(long_var_name);
console.log(result1, result2, result3);
Using this example you can compare it with the First, Second and Third method.
This question already has answers here:
What do empty parentheses () after a function declaration do in javascript? [duplicate]
(4 answers)
Closed 9 years ago.
I didn't find a post asking for a pattern similar to this one, sorry if I missed it.
Anyway, I'm repeateadly seeing this pattern in many jQuery plugins or scripts:
(function () {
...........
}());
What's its purpose? Does it have a name?
Thanks!
It's also known as an Immediately Invoked Function Expression
Ben Alman has a good article covering IIFE usage, and why "self-executing anonymous function" isn't the best terminology:
One of the most advantageous side effects of Immediately-Invoked
Function Expressions is that, because this unnamed, or anonymous,
function expression is invoked immediately, without using an
identifier, a closure can be used without polluting the current scope.
[... T]the term “self-executing” is somewhat misleading, because it’s
not the function that’s executing itself, even though the function is
being executed. Also, “anonymous” is unnecessarily specific, since an
Immediately Invoked Function Expression can be either anonymous or
named. And as for my preferring “invoked” over “executed,” it’s a
simple matter of alliteration; I think “IIFE” looks and sounds nicer
than “IEFE.”
It's a an immediately invoked function expression (Fiddle):
(function () {
alert("pee");
}());
It is an Immediately-Invoked Function Expression.
It's useful for creating a scope for its contents to enjoy.
It's similar to this:
function myFunc() {
//code
}
myFunc();
But there are 2 differences:
The function is named here
The above code is a function declaration, different from a function expression. 'myFunc' above gets stored as a variable unless you use it as an expression, like so:
foo(function myFunc() {
//code
});
Then it will not get stored as a variable.
It's a immediately-invoked function - as soon as you declare it, it gets evoked.
The () syntax in Javascript means "call this function with whatever arguments are between ( and ). Since there isn't anything between the parentheses in your example, no arguments are supplied to the function call; but if you need to supply arguments, you can do something like this:
(function foo(arg1, arg2) {
alert(arg1 + " " + arg2);
})(3, 5);
Which will immediately call foo() and pass in 3 and 5 as the two arguments.
This question already has answers here:
What is the (function() { } )() construct in JavaScript?
(28 answers)
Closed 8 years ago.
I started JavaScript programming last month, i know basic syntax like objects, functions, class, string, array, property. Now i was puzzled on given syntax.
Syntax:
(function(){
"use strict";
})();
My question is, why two parenthesis( one contains 'function' and another "empty" ) are included in the definition? can some one help me why we use this?.
That will create an anonymous function and then immediately execute it.
In this case that function has a single line..."use strict".
That code doesn't have any net impact on the world. What happens is:
The parenthesized function is instantiated;
The final () cause that function to be called;
The "use strict" constant turns on "strict" mode;
The function returns.
What you have there is a self-invoking function.
It pretty much is exactly that, a function which immediately gets called. To accomplish that, we need a function expression, not a function declaration. To achieve that, we can do certain things, one of those is, to put the whole expression in parenthesis
(function() {});
this statement creates a function expression. Now all we have left to do is, to invoke that function by appending additional function parenthesis, like we would do with any function
(function() {})();
You can also put the function parenthesis into the whole statement, it makes no difference
(function() {}());
Another option to bring a function into an expression form is by using ! or + signs infront of it
!function(){}()
Anything goes, as long we create an expression, we can't invoke a function declaration like that
function foo(){}() // syntax error
This is a self-invoked anonymous function (or immediately invoked function expression, also known as IIFE), a pattern that in this case exists just to produce a closed scope.
Apparently, they don't want "use strict"; turning on strict mode for the whole file, or when minified and concatenated to other files, turning on strict mode on included libraries, etc. Amazon had a problem with this a while back. Since then, it's been recommended best practice to keep "use strict" in function scope, and this function exists solely for that purpose.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
What does this “(function(){});”, a function inside brackets, mean in javascript?
javascript anonymous function
(function())()
this is used in many js library like jquery,YUi
Thats called Module Pattern. The idea is to have an encapsulated module, that cannot conflict with any other modules you or someone else has created. You can create public and private methods within that module.
See: Js Pattern
I'm not sure what (function())() means, but I'll work on the assumption that you meant (function() { … })(). It is roughly the same as:
f = function() { … }; // Define a function.
f(); // Call it.
The only difference is that it does so without requiring a variable.
It is an anonymous self executing function. It is anonymous, because it is not named, and self executing, so it runs (there would be no other way to run an un-named function).
It is particularly useful to enclose a discreet module of code, because it acts as a closure preventing variables leaking into the global namespace.
You're immediately calling an anonymus function with a specific parameter.
An example:
(function(name){ alert(name); })('peter') This alerts "peter".
In the case of jQuery you might pass jQuery as a parameter and use $ in your function. So you can still use jQuery in noConflict-mode but use the handy $:
jQuery.noConflict() (function($){ var obj = $('<div/>', { id: 'someId' }); })(jQuery)
It simply executes the code wrapped in parentheses right away (the first block returns a function, the second pair of parens executes it).
Take for instance these two snippets:
function foo() {
print 'foo';
}
(function() {
print 'foo';
})();
The first won't do anything until you call foo(); whereas the second will print 'foo' right away.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
What is the purpose of wrapping whole Javascript files in anonymous functions like “(function(){ … })()”?
Hello all,
I have seen several JavaScript files using this notation:
Start of JavaScript file:
(function() {
// All functions go here.
// Can someone say what the wrapping nameless function is used for?
})();
Also with the prototype library, this seems possible:
function $() {
// Prototype $-wrapping function.
}
Can someone please explain the above two code fragments, their uses and their differences? Some keywords which would help me find more about this notation/technique (how it is named) would be helpful too so I can run a Google search on it... :)
Thanks!
In your first example, people surround their code in an anonymous function for scoping reasons, to avoid global namespace cluttering. That weird parentheses syntax is used to define and execute the function all in one step; the () at the end has the meaning of executing the function itself.
So inside that anonymous function you could define function apple(){} and it would only be accessible inside that anonymous function. This is good if you're making a library and want only certain things to clutter your global namespace.
Your second example is just a simple function called $. Many libraries like to use this name because it's short and concise, and since you need to type it every time you want to reference the libraries namespace, the shorter, the better.
I searched for "javascript wrapping function" and the first hit was this, which says:
This method doesn't add any new symbols to the global or LIB spaces.
I don't understand the second part of the question: function $() { ... } isn't a "nameless" function: it has the name $! If you like functions named $ it's the most straightforward way I know of to make such a thing.
An annonymous function is defined
function() {
}
and then immediately called
()
The extra () enclosing the function is to force the interpreter to treat the function as an expression. Javascript treats any statement starting with the function keyword as a declaration so it could not otherwise be immediatly called.
The purpose is to avoid polluting the global namespace. All variables defined in the function will be local to the function.
Google for module pattern.
retracted in favor of answer to: What is the purpose of wrapping whole Javascript files in anonymous functions like “(function(){ … })()”?
First one is called immediate function. You can read more about this function pattern here.