Javascript challenge question doubt

Question

var foo1 = function(){
console.log("a");
}()
var foo2 = function(){
console.log("a");
}
var foo3 = function(){
foo2();
}
if(foo1) foo3;
console.log(typeof foo1);

what is that () means in line 3 , and why foo1 is undefined

https://code.sololearn.com/Wch8fZQTade4

Answer 1

@Morpheus on line 1 it's an expression, and you can do this. But when we write smth like:

function foo () {
lalala;
}

It's a statement, and if you put here "()", then syntax error occur.

Answer 2

foo1 is undefined because function on line 1 returns nothing (you call in on line 3 using "()")

Answer 3

@Morpheus you're welcome.

Answer 4

@Morpheus yes, it's a really good thing, in the global scope will be exist only these variables that we want.

Answer 5

im not a js expert but:
- these () mean "call the anonym function" and for this that "a" be printed
- foo3 is undefined because it assume return value of anonymous function call (the dont returning nothing for js rule return undefined automatically)

Answer 6

I would only use it to self invoke functions 😅, looks like it serves bigger purpose

Burey puts question like this in challenges for a purpose, its serving me now

Answer 7

@silent got it , thx

Answer 8

I couldn't understand what's the use of it, but got some ideas from its use in the module pattern.

https://toddmotto.com/mastering-the-module-pattern/