This question already has answers here:
What is the (function() { } )() construct in JavaScript?
(28 answers)
Closed 5 years ago.
Could I get an explanation of the follow code snippet?
(function()
{
alert();
})();
This looks like an anonymous function and the alert() function gets executed. I don't understand the semantic meaning of the outer parentheses. What does this part of the snippet mean?
(
)()
this represents the immediately executable function. in easier way, it means that function being declared and called/executed simultaneously.
Related
This question already has answers here:
What is the (function() { } )() construct in JavaScript?
(28 answers)
Closed 2 years ago.
I came across with a piece of code with new syntax for me, What this syntax means in js? I mean this parentheses at the beginning:
(function () {
//...
})()
It's called IIFE
basically, you can define a a function and invoke it immediately without declaring a name for it.
This question already has answers here:
What is the (function() { } )() construct in JavaScript?
(28 answers)
What does (function($) {})(jQuery); mean?
(6 answers)
Closed 8 years ago.
What does (function($) {})(); mean?
Its an Immediately-Invoked Function Expression (IIFE).
It means that the code between the curly braces will be executed as soon as its parsed and inside a closure. This means that any variables declared inside the function body with var will be discarded from memory after the function is finished executing. This is a way to isolate code and prevent namespace polution. You can also use this to rename variables for a particular scope:
For example, consider jquery:
(function($){
//inside the closure, jquery can be accessed using '$'
$(...)
})(jquery);
or
(function(customJqueryName){
//inside the closure, jquery can be accessed using 'customJqueryName'
customJqueryName(...)
})(jquery);
Check out closures: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Closures
IIFE: http://benalman.com/news/2010/11/immediately-invoked-function-expression/
It's an anonymous inline-function, which will be called just after definition.
This question already has answers here:
What is the purpose of a self executing function in javascript?
(21 answers)
What is the (function() { } )() construct in JavaScript?
(28 answers)
Closed 8 years ago.
I see this in some HTML files that use jQuery, at the bottom:
(function() {
setTimeout(function(){window.scrollTo(0,0);},0);
})();
What does it mean to put the whole function in round brackets?
The code you gave as example is a self-executing anonymous function.
You can read more about them here.
Relevant text from that article:
What’s useful here is that JavaScript has function level scoping. All variables and functions defined within the anonymous function aren’t available to the code outside of it, effectively using closure to seal itself from the outside world.
(function() {})(); means it is self executing anonymous function. It get called immediately when java script get rendered. More details you can search it.
setTimeout is a function which accepts two parameters:
First parameter: A function
Second parameter: an integer value in milliseconds.
By calling the setTimeout function, the function from first parameter will be called/invoked after the amount of time specified in the second parameter.
This question already has answers here:
What is the (function() { } )() construct in JavaScript?
(28 answers)
Closed 9 years ago.
I'm trying to understand the difference between :
var x = function () { ....}
(function () { ....} ) ();
I get it that the first function will put the results on x.
that and when exactly the second one will be fired? and why do i need the (); at the end?
This is an example of the Immediately-invoked function expression.
The function is executed immediately because () is how JavaScript calls functions. The syntax might be confuse you, because the function does not have a name, but ( function(){} )() just immediately calls the function with no arguments.
This question already has answers here:
Javascript anonymous function call [duplicate]
(4 answers)
Closed 9 years ago.
How come
function(){ alert("test123");}()
produces SyntaxError: Unexpected token (
while
!function(){ alert("test123");}()
alerts "test123"
?
It's because by adding ! sign you convert the declaration into an expression and invoke it immediately.
By enclosing your function into brackets you will make first example working without errors:
(function(){ alert("test123");})()
To make it clearer you can think about first expression as something like:
if (false || !function(){ return false; }())
And as #zerkms noticed there is a complete explanation of Immediately-invoking functions.