[SHOwnsYou]

From the article--

let x = 'outer';

function test(inner) {

  if (inner) {

    let x = 'inner';

    return x;

  }

  return x; // gets result from line 1 as expected

}

test(false); // outer

test(true); // inner

This makes it seem like let creates global variables. Why would you want to return a variable from outside the function? Doesn't that create massive overhead in terms of keeping track where variables are initially set? Easy to understand in this example, but what if let x = 'outer'; is defined at the top of a 5000 line script and this function appears near the bottom?

Edit: Turns out I don't know how to format code. This is in the first example of section 3.1 Block Scope Variables.

[Meegul]

If you were to then reference 'x' from another block of code, say in another <script> element in the case of web development, 'x' would not be a defined variable, whereas with 'var', it would be.

This is mostly just a case of 'let' restricting a variable to the block it is in, and the child blocks. In your example, `let x = 'outer';` is sort of acting like a global variable, but the importance is that if another script were to be running, it could not access that instance of 'x'.

[Roboprog]

Ehw. Yeah, I sort of assumed that you had a top level function / IIFE (in a .js file, FWIW) in which the var's were nested.

Somebody writing stuff, into the global namespace, directly in <script> tags, has bigger problems :-)

[SHOwnsYou]

Ahh, I get it, Thank you! In the same way var scopes to window if defined outside of a function, let scopes it to the current script block. That is very neat.

I'll read more into uses of let over var. Function level scoping a la var feels like less mental overhead, but as I read more I'm sure my opinion will change.