Javascript Es6 'let' And 'var' - Unexpected Behavior Inside Function With Argument Name Matching Redeclared Variable

Please note this is not duplicate of existing var vs let scope. I'm aware of the scope of var and let declarations and differences. But below scenario I could not justify with the

Solution 1:

The var declaration syntax is original to the language, and has fairly permissive rules. The let and const declarations are newer and more strict. You cannot re-declare variables with let or const no matter how they were declared in the first place. And if a variable is declared with let or const, a subsequent var declaration is also an error.

Declarations via let and const will not allow references to the variables before the declaration; that's why you get the error mentioned in your first example. In other words,

console.log(x);
let x = 0;

is an error because x is referenced before the declaration.