Scope Functionality Testing Thing

scope.js

let f;
let y;
let z;
let i = 0;
const j = ()=>{
  let s = ++i;
  f = f ?? (() => s);
  z = ()=>s++;
  y = y ?? z;
}
j();
if (i !== 1) throw new Error('i did not increment to 1 after j was called (i is in root scope)');
if (f() !== i) throw new Error('f did not return value of i');
j();
if (f() !== 1) throw new Error('Scoped variable \'s\' changed after changing i (does j\'s scope leak?)');
if (f() === i) throw new Error('Global variable \'i\' has same value as \'s\' after incrementing');
y();
if (f() !== 2) throw new Error('Scoped variable \'s\' did not change after incrementing in initial scope');
z();
if (f() !== 2) throw new Error('Scoped variable \'s\' changed in initial scope after changing \'s\' in 2nd j() scope');

scope.lua

local f;
local y;
local z;
local i = 0;
local j = function()
  i=i+1;
  local s = i;
  f = f or function()return s;end;
  z = function()s=s+1;end;
  y = y or z;
end;
j();
if (i ~= 1)   then error('i did not increment to 1 after j was called (i is in root scope)'); end;
if (f() ~= i) then error('f did not return value of i'); end;
j();
if (f() ~= 1) then error('Scoped variable \'s\' changed after changing i (does j\'s scope leak?)'); end;
if (f() == i) then error('Global variable \'i\' has same value as \'s\' after incrementing'); end;
y();
if (f() ~= 2) then error('Scoped variable \'s\' did not change after incrementing in initial scope'); end;
z();
if (f() ~= 2) then error('Scoped variable \'s\' changed in initial scope after changing \'s\' in 2nd j() scope'); end;