Salesforce JavaScript Developer Practice Exam

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

1. It will succeed and store the latest value.

2. It will throw a SyntaxError.

3. It will keep the first declared value.

4. It will result in an implicit global.

The correct answer is: It will throw a SyntaxError.

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.