Given javascript syntax will do what?

Question

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?.

above link is very good...Thanks a lot. – Ashif Feb 08 '13 at 00:00 — Ashif, Feb 08 '13 at 00:00

score 2 · Answer 1 · answered Feb 07 '13 at 23:31

2

That will create an anonymous function and then immediately execute it.

In this case that function has a single line..."use strict".

answered Feb 07 '13 at 23:31

Justin Niessner

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score 2 · Answer 2 · answered Feb 07 '13 at 23:31

2

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.

answered Feb 07 '13 at 23:31

Pointy

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Plynx · Answer 3 · 2013-02-07T23:39:07.657

1

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.

edited Feb 07 '13 at 23:39

answered Feb 07 '13 at 23:31

Plynx

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I don't mean to pick on you but a popular alternative term is "immediately-invoked function expression" (IIFE), which is a bit more accurate since the function doesn't really invoke itself. – Pointy Feb 07 '13 at 23:32
@Pointy I actually googled both expressions before writing the answer to see which would lead to more useful results, but you're right. – Plynx Feb 07 '13 at 23:34
I called them that for quite a while before somebody asked me how exactly the function managed to execute itself :-) – Pointy Feb 07 '13 at 23:35
@Pointy :O YOU'RE RIGHT! – Plynx Feb 07 '13 at 23:39

score 1 · Accepted Answer · answered Feb 07 '13 at 23:34

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

Given javascript syntax will do what?

4 Answers4