Thanks for the comment.
In case of let, redeclaring a variable in the same scope will produce error.
What I have read from stack overflow is var is function scoped and let, const etc are block scoped. Also tried coding some example, my conclusion is you can have the same named variable with var keyword in another function, that means it is limited to function scope. And you can have same named variable with let keyword in another block, that means it is limited to block scope.
function - What is the scope of variables in JavaScript? - Stack Overflow