What does function() do?

JavaScript
#1

I tried to look this up but idk what is happening or what this is actually called.

'use strict';
let printNumTwo;
for (let i = 0; i < 3; i++) {
  if (i === 2) {
   printNumTwo = function()
     return i;
   };
  }
}
console.log(printNumTwo());
// returns 2
console.log(i);
// returns "i is not defined"

Also in this case i is returning 2, and if “strict” and let is not used i returns 3. Would this be the case if printNumTwo = i and then used in console.log?

I guess the main question is what is function() doing and what is the difference between calling printNumTwo when function() is used, compared to printNumTwo when it is set to a value and called?

Thanks for any insight.

#2

The second part of your question, that is, “i is not defined”,for that you need to read about variable scopes. There are mainly two types of scopes: global and local. In this case, i is local to the scope of for loop. That means it is just available for the for-loop and as soon as the loop ends, the variable “i” is no longer accessible by the program.

The first part of your question in which you have declared a function within the for-loop and calling that function is a bit something new for me and interesting. I have never seen something like this before.

#3

Okay. So I found out a similar issue solved by someone in FCC forum. Let me share the link.

#4

Cool thanks for the replay.

I went back and read the tutorial and I missed where it said that var was a global variable. I thought that it was similar to C and would only be global if declared a certain way or in a certain area of code. That isn’t the case.

let is the local version. So even if a counter is called in a loop with var it will be global.

I have been able to find a few things on function(). It is called anonymous function I believe.

Here is a link: https ://en.wikibooks.org/wiki/JavaScript/Anonymous_functions

I believe it sets printNumTwo to an unnamed function. Only thing now is I don’t know if when called if printNumTwo() is equal to i or if it is simply a function now that only returns i. I guessing the latter but I still don’t know enough js to know for sure.

1 Like
#5

It’s called a closure (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Closures)
because the function closes around the variable, so the variable is within its scope, even when its not in the scope of where the function is being called from.

#6