Writing javascript function inside a function [duplicate]

Question

This question has already been answered:

There is such code:

var f = function() { this.x = 5; (function() { this.x = 3; })(); console.log(this.x); }

Why the function inside the function is written like this:

 (function() { this.x = 3; })();

And why can not write like this:

 function() { this.x = 3; }

?

oh how bad everything is, and where did you find such a code?
Alexey Ten, my question is not very similar to what they took off the source.
firstly not a duplicate, and secondly the answers are not satisfied.
@Ilnyr, no, in this edition your question is an absolute duplicate of the one provided by the link.
And in this source, I don’t see any mention of this in the "wrapper"

Answer 1 · 2016-07-07T12:30:55

This is called a "wrapper", you declare a function and immediately call it. In the second case, I had to write this:

 var f1=function(_this) { _this.x = 3; } f1(this);

The point is that in the "wrapper" this accepts not the value of the function itself, but the value of the external function.

which means in the "wrapper" this takes not the value of the function itself, but the value of the external function.
@iKest, the code given in the answer is not similar to what is given in the question

Reported as a duplicate by Grundy , user194374, aleksandr barakin , Bald , fori1ton July 8, '16 at 15:41 .