javascript - Does 'let' override a global declaration and throws a ReferenceError?

Question

I was going through the Difference between var and let documentation example and was testing that when an undeclared variable is invoked, the global scope automatically provides a declaration for it (that's why the following snippet does not throw an error in any of the variables):

x = 3;
console.log(x);

(function() {
  y=x+39;
})()
console.log(y);

Answer 1

Did you have a look at the let docs at MDN? They describe a temporal dead zone and errors with let.

ES6 does hoist a let variable to the top of its scope. Differently to var variable, when using let you must not access the variable before it is declared. Doing so fail with a ReferenceError (a.k.a. let's temporal dead zone).