Salesforce JavaScript Developer Practice Exam

What will be the output of console.log(x); let x = 10;?

1. 10

2. undefined

3. ReferenceError

4. NaN

The correct answer is: ReferenceError

When you attempt to log the value of `x` to the console before it has been initialized, you will encounter a `ReferenceError`. This occurs because `let` declarations are block-scoped and are not hoisted in the same way that `var` declarations are. While `var` would allow you to access the variable and receive `undefined`, `let` does not allow access to the variable until the declaration has been encountered in the code. In this case, `console.log(x)` is executed before the line `let x = 10;` is reached, leading to a situation where `x` remains uninitialized and unreferenced. As a result, JavaScript raises a `ReferenceError`, indicating that `x` is not defined at the point of the console log. This behavior is part of the temporal dead zone concept in JavaScript, which prevents access to variables before they are declared.