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?.

Answer 1

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