In Javascript scopes are defined at function level, if declared with var, on the other side es6 let/const define scope at a block level (e.g. in an if-block, or for loop)

js-es6-block-level-scope.js

console.clear();
if (true) {
	let insideJoke = 174; // let used -> block's scope
	const anotherInsideJoke = 100; // const used -> block's scope
	var thisIsACommonJoke = 42 // var used -> scope to outer scope (global)
}
console.log('thisIsACommonJoke', thisIsACommonJoke); // ok, global scope
console.log('insideJoke', insideJoke); // error: out of scope