Can you help me explain how this code works in JavaScript?

Question

function fib(num){
if (num<=2)
return 1;
return fib(num-1)+fib(num-2);
}
alert(fib(6));

/*
This code output 8.
I'm learning programming by myself about 1 month. I try so hard to understand how it work but I can't. If it too long to write somethings easy to explain it so please tell me what I have to learn to understand that code. Thank you so much.
*/

Answer 1

That is a challenge question in JS course, I'm not create that code so I didn't figure out even .. You know, but I think I need to learn more about something related to "self-invoking" of function. Thank for your help, I can see you are a enthusiastic person. Best luck to you:)

Answer 2

here is your question 👇👇but it outputs undefined

https://code.sololearn.com/W1LNSuyz4A0k/?ref=app

i dont know if you framed the question well but i tried my best to answer.....even though am not quite good in this stuff