What will happen if you attempt to use let for re-declaring a variable within the same scope?

In JavaScript, using the let keyword for variable declaration creates a block-scoped variable. This means that if you attempt to re-declare a variable in the same scope using let, it will lead to a SyntaxError.

The reason for this behavior is that let provides a stricter scope control compared to var, which allows for re-declaration in the same scope. The introduction of let was designed to reduce issues caused by variable hoisting and accidental re-declarations that can lead to bugs in code. Therefore, when you try to declare a variable with let that already exists in the current scope, JavaScript will not allow it and will throw a SyntaxError to maintain the integrity of the scope.

Understanding the block scope and the rules associated with variable declaration in JavaScript is essential for writing robust code and for avoiding common errors, particularly in larger applications or when working with closures. This is why attempting to use let to re-declare a variable in the same scope specifically results in a SyntaxError.