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';
$('#bookelement').html(Book);
})(jQuery);
These all are self executing functions. Now days also known as Immediately Invoked Function Expressions (IIFE).
First two are exactly same with slightly different syntax and third is passing a parameter as jQuery object.
In fact, all three are self executing function's and ti really depends on what you are needing to do.
The only difference between is between 3. 1 and 2 are the same.
The difference with 3 is that you are passing a reference to jquery as an argument. Now all functions inside this annoyomus function have access to jque
All of these are example of self invoking function.
This will give you a clear view:-
var my_func = function(){
var internal_var = "Hello";
return internal_var;
};
var my_func2 = function(name){
var internal_var = "Hello";
return internal_var;
};
var long_var_name = "I can be some object or number or object or array";
var result1 = (my_func());
var result2 = (my_func)();
var result3 = (my_func2)(long_var_name);
console.log(result1, result2, result3);
Using this example you can compare it with the First, Second and Third method.
What are the difference among -
First :-
(function () {
var Book = 'hello';
}());
Second:-
(function () {
var Book = 'hello';
})();
First and second are similar some how in work..
Third :-
(function ($) {
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.
Recently I was reading someone else's code, and came across this:
// Semicolon (;) to ensure closing of earlier scripting
// Encapsulation
// $ is assigned to jQuery
;(function($) {
// DOM Ready
$(function() {
...
});
})(jQuery);
I understand the point of the leading ;, And I understand that $(function() { is the same as document ready, but what is the point of adding function($)?
I understand it's a closure, but since this is always being called at the global scope, it seems like you don't need to bother with it. The $(function() { will use the same global object either way, no?
Is it to safeguard against something, or is it a best practice for another reason?
It's a common structure for a jQuery plugin. It safeguards against the $ identifier having been overwritten and used for something else. Inside the anonymous function, $ is always going to refer to jQuery.
Example:
$ = "oh no";
$(function() { //Big problem!
//DOM ready
});
By introducing a new scope, you can ensure that $ refers to what you expect it to:
$ = "oh no";
(function($) { //New scope, $ is redeclared and jQuery is assigned to it
$(function() { //No problem!
//DOM ready
});
}(jQuery));
The main reasoning behind this is that numerous other JavaScript libraries use $ as an identifier (e.g. PrototypeJS). If you wanted to use both Prototype and jQuery, you need to let Prototype have its $ identifier, but you probably don't want to write out jQuery every time you want to call a jQuery method. By introducing a new scope you allow jQuery to have its $ back in that execution context.
The code sample you've provided is an example of a Self-Invoking Function:
(function(){
// some code…
})();
The first set of parentheses defines a function: (an anonymous function wrapped in parentheses)
(function() {})
That defines the anonymous function. On its own, it doesn't do anything. But if you add a set of parentheses () after the definition, it's the same as the parentheses used to call a function.
Try this out:
(function(message) {
alert(message);
})("Hello World");
That creates a function which accepts a parameter, and displays an alert box containing the provided value. Then, it immediately calls that function with a parameter of "Hello World".
In your example, a self-invoking function is defined. It accepts a parameter, which is named $. Then, the function is immediately called, with a reference to jQuery being passed in as the argument.
This is common if you want jQuery to operate in noConflict() mode (which removes the global reference to $).
In noConflict() mode, you can still access jQuery via the jQuery global variable, but most people would rather use $, so this self-calling function accepts the global jQuery variable as a parameter named $ in the scope of the function, which leaves you free to use the $ shortcut within the self-invoking function while having jQuery operate in noConflict() mode to avoid clashes with other libraries that use $ in the global scope.
Hope this answers your question!
Is this jQuery code
(function(jQuery){
})(jQuery);
equivalent to
$(document).ready(function () {
});
If yes, what are the differences between the two? If not, what does the first do?
EDIT:
Thanks everybody. Most response are similar with different flavours and sample
They are not equivalent.
Your first example is an Immediately-Invoked Function Expression (IIFE). It creates a closure around locally defined variables.
Your second example specifies a function to execute when the DOM is fully loaded. It is used to ensure that all element nodes in the DOM are available before executing the enclosed code. This is also a closure.
Both examples use anonymous functions.
It is worth pointing out that it is good practice to use both of your examples, like so:
(function($){
// locally-scoped, DOM-is-NOT-Ready-code here.
$(function () {
// your locally-scoped, DOM-is-ready-code here.
});
}(jQuery)); // note that I've moved the invocation into the parens
// that contain the function. This makes JSLint happy!
Absolutely not, the first one is a self-executing anonymous function and the second is the ready handler.
(function(jQuery){
//jQuery in this scope is referencing whatever is passed-in
})(jQuery);
So, the jQuery inside of the function isn't necessarily the same jQuery outside the function. But you typically do not want to mix-n-match global variable names with local ones.
Take this example:
(function(obj) {
alert(obj);
})('Hello');
This defines a function, then immediately invokes it, passing in "Hello"
$(document).ready(function () {
});
is equivalent to this:
$(function() {
});
The first snippet is an immediately invoked anonymous function which creates a local scope:
(function() {
var x = 2;
})();
alert(x); // undefined
No. The first one isn't really doing much. Just separating any variables inside from the surrounding scope, and creating a local jQuery variable inside.
The second one passes a function that is run after the DOM is ready (in other words after the <body> has loaded).
A common equivalent to:
$(document).ready(function () {
});
is:
$(function () {
});
which does the same thing.
While this:
(function(jQuery){
})(jQuery);
is often written as:
(function($){
})(jQuery);
so that the $ variable is no longer a global variable. Useful if the global $ variable is already in use.
Not at all. The first one is a closure - a function that you create and then immediately call. However, typically you would combine the two like this:
(function($) {
// use the $ variable
$(document).ready(function(){
// ...
});
})(jQuery);
By creating the closure you are renaming "jQuery" to "$" just locally for that block of code. The reason why you use the closure syntax is so that you can use the $ variable even though it might not be defined as a jQuery object in the global scope (i.e. some JavaScript frameworks like prototype use $ as a variable).
Whenever you write a jQuery plugin you should enclose all jQuery code in this kind of closure so it doesn't interfere with any other JavaScript frameworks. If you aren't writing plugins and you don't use any other JavaScript frameworks you probably don't have to bother enclosing your code in a closure.
I'm hoping someone can explain the following usage of JavaScript.
I have a page with a script that looks like this:
(function($){
// code
// and stuff
})(jQuery);
I'm trying to understand what this code does, specifically:
The opening parenthesis at the start
The usage of the $ symbol
The jQuery in parentheses at the end
thanks!
This is an anonymous function.
The specific example you provide is usually used when jQuery (which uses the "$") is conflicting with another library (prototype also uses "$").
What this does is say that whenever "$" is used within the function, it is to reference the jQuery object.
Normal:
$("foo").doStuff()
Conflict avoidance:
jQuery("foo").doStuff()
Using anonymous function to avoid conflict:
(function($){
$("foo").doStuff();
})(jQuery)
At the highest level, it is declaring a function and invoking it in the same statement.
Let's break it down into component parts:
First, we can use $ as an argument/variable name in a function, just like anything else:
function foo($)
{
alert($);
}
foo('hi'); //alerts 'hi'
Second, we can assign a function to a variable:
var foo = function($) {
alert($);
}
foo('hi'); //alerts 'hi'
Finally, we don't have to give functions names - we can just declare them. We wrap them in parenthesis to encapsulate the entire function declaration as a var, which we then call (just like above):
(function($) {
alert($);
})('hi');
In your case, jQuery is some object being passed into the function as the $ parameter. Probably the jQuery library root object, so you can call functions on it.
The parenthesis wrap the anonymous function so it can be called right away with the parameter being a reference to jQuery
$ is a valid variable name in JavaScript, so many frameworks use it for brevity. By including it here as the function argument, you're saying that you want to use $ as an alias for jQuery. This lets you keep your code as short as possible and save your user's bandwidth.
Answered in the first part - you're sending a reference to the jQuery object/framework to your anonymous function.
Briefly:
This declares an anonymous function which accepts one argument, referred to by the local variable name of $, and then immediately calls the function passing as the first argument the jQuery object.
Less briefly:
In javascript a function is declared like this:
function foo(arg1, arg2){
}
Later the function foo can be called:
foo("arg 1", "arg 2");
But in javascript functions are first class citizens; you may, if you choose, store a function in a variable. When doing this the variable name is the function name, so you write it like this:
var foo = function(arg1, arg2){
};
The trailing semicolon is required because a variable declaration (and assignment) is a statement. Later, the function foo can be called:
foo("arg 1", "arg 2");
The advantage here is that you can pass the function to another function, or store it in an array, or whatever. Functions of this sort are called anonymous functions (because they have no function name as such).
Inside the anonymous function foo, as seen above, you can declare local variables which remain withing the scope of that function and do not exist in the scope in which the function was declared. For example, the local arg1 and arg2 variables don't exist in the scope of the variable foo (but they do exist within the anonymous function stored in foo).
This trick allows us to create a private block in which we control what things are named without worrying about stomping over someone else's namespace.
You could write the example you provided as follows:
var foo = function($){
};
fn(jQuery);
Which is the same thing, but has that ugly intermediate variable. What may not be obvious is that the declaration of the anonymous function "returns" a function reference which can be invoked later... or at the same time, merely by adding the function call syntax of ().
What the code is doing is defining an anonymous function, which creates a private scope, and then immediately calling it without storing in a variable. Like this:
function(arg1){
}("arg 1");
I am not entirely sure why there's an extra set of parentheses arroudn the anonymous function definition, but they at least make the code a little more readable/logical. You are merely passing an argument to the result of the parenthetical expression, which happens to be a function:
(function(arg1){
})("arg 1");
All of tis allows jQuery to have a globally-scoped variable named jQuery, but also allows you the user to use the shorthand of $ without conflicting with other javascript frameworks which use the same name for other things.
Let’s first look at the inner function declaration:
function($){
// code
// and stuff
}
This is an anonymouse function declaration with one parameter named $. That function is then wrapped in parenthesis and called by appending (jQuery) to it with jQuery as parameter.