This question already has answers here:
What does the exclamation mark do before the function?
(8 answers)
Why use NOT operator on anonymous function call? (a la Knockout 2.1.0) [duplicate]
(2 answers)
Closed 9 years ago.
Did anyone know the code which define like this:
!function(window, undefined) {
// do something
} (window)
By searching in google, I can understand the syntax like:
function(window, undefined) {
// do something
} (window)
But I don't figure out any article about the syntax have "!" operator.
The ! operator is there so the function is parsed as an expression, rather than a declaration. Since a declaration cannot be invoked, your second example is a syntax error.
A more commonly seen form is to enclose the function in parentheses:
(function(window,undefined) {
// do something
}(window));
That has exactly the same effect, as does the use of any unary operator.
It might be like this.
!(function(window, undefined){ /* some code */ })(window);
(function(window, undefined){ /* some code */ })(window);
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)
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.
This question already has answers here:
What is the (function() { } )() construct in JavaScript?
(28 answers)
Closed 7 years ago.
I am learning about JavaScript functions on MDN
I came across an example that looks similar to this:
var saySomething = ( function(){console.log("hello")} )();
I have also seen this in the jQuery source.
I have not found any explanation of this style of function calling/definition on the MDN function reference.
I know from running the code that it calls itself immediately upon interpretation by the JavaScript engine.
Is this the Grouping Operator in action? Where it says:
First evaluate the body of this function and return it
Since the parentheses () immediately follow it it gets called ?
Google "Immediately Invoked Function Expression" or "IIFE".
The general syntax looks like this:
(function(){
// do something here
})():
Sometimes you'll see arguments passed in as well. It's basically used to wrap your code so none of your variables leak out into the global namespace.
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.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
What does the exclamation mark do before the function?
! preceding function in javascript?
javascript function leading bang ! syntax
I've been seeing this pattern a little bit recently in javascript:
!function () {
// do something
}()
what does the bang in front of the function keyword supposed to do? I can't seem to find anything about it on the intertubez.
function () {
// do something
}();
This is an immediately invoked function declaration. A function declaration can not be immediately invoked; it is a syntax error.
To get around this syntax error, most people enclose the IIFD in parens to force it to be an expression instead (IIFE).
(function () {
// do something
})();
In this case, they added an exclamation point instead.