what's meaning the symbol "!" before a function ? return something different ?

Question

one exemple :
var a=5;
!function (x)
{a=x;}(7)
alert(a);

Answer 1

! is the boolean not operator, which you probably know. Calling a function results in a value (in this case undefined). The side effect still happens, so a will be assigned 7, but then nothing happens. You can rewrite it like this:

a = x;
!undefined

!undefined is true, but since it isn't used at all, it won't matter.

Answer 2

https://code.sololearn.com/Wt2b0KJCm2kS/?ref=app

Answer 3

first thank ODLNT and Airree for your answers.
I understand better.

So, it was a question in JavaScript challenges... i just would understand what's happen in this case (i hope it will not use in some crazy real program code :p)