Why can't I use ++ Operator in Pass Arguments to Avoid External Dependence in a Function

JavaScript
1

Tell us what’s happening:
I know this is early on so I don’t quite understand the purpose of the functional programming but so far, 3 lessons in, it sounds like the point is to have a function that doesn’t alter something outside of it. If so, why can’t I just use the increment operator ++ in my function? It still doesn’t change the global value but it’s considered wrong.

Your code so far


// the global variable
var fixedValue = 4;

// Add your code below this line
function incrementer (myValue) {
  
  return myValue +1;
  //return myValue++; is considered wrong
  //Add your code above this line
}

var newValue = incrementer(fixedValue); // Should equal 5
console.log(fixedValue); // Should print 4

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36.

Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/functional-programming/pass-arguments-to-avoid-external-dependence-in-a-function

2

It’s because the post incrmentor isn’t exactly the same as + 1. When you do return myValue++ it actually adds 1 after the return executes.
Either

myValue ++;
return myValue;

or

return ++myValue;

will work. If you want to dig into it, you can research the difference between a pre incrementor and post incrementor.

3

I realize that but the scope of it is still within the function and won’t alter the global variable.

4

It’s true that it doesn’t change the global variable. Are you expecting it to?

5

No I’m just curious why it fails even though it technically fulfills the requirements of the assignment and gives the correct response. Is it technically considered imperative to use ++, it’s not considered common practice in functional programming, it’s impolite, or it’s just not something the test was expecting?

Thank you for your responses by the way?

6

It doesn’t fulfill the requirements though. It will not return the correct value if you use a post incrementor, which is what I was originally trying to explain.

7

Ah, so you are right! ++MyValue works as expected though.
Thanks for your help