Test your knowledge: JavaScript Variables, Bindings, and Scope

Review

1. Which declaration fits a score that starts at 10 and is reassigned after each round?

   let creates a mutable lexical binding, so it can be reassigned. const does not permit reassignment of its binding.
2. What does const guarantee about its binding?

   const creates an immutable lexical binding: the name cannot later be assigned a different value. That does not mean an object reached through the binding is deeply immutable.
3. What does this code print first? let message; console.log(message);

   A let binding without an initializer receives undefined when the declaration is evaluated. No later assignment has happened yet.
4. After this block finishes, which binding is still available? { const inside = 7; }

   The const declaration is block-scoped, so the binding named inside is not available outside that block.
5. With const name = "Maya" and let lessons = 3, what does `Hello, ${name}. You have ${lessons} lessons.` produce?

   Template literals evaluate each substitution expression and place its resulting value into the string.
6. Which statement best distinguishes declaration from assignment?

   A declaration introduces a binding, while an assignment evaluates a value and stores it through an existing mutable binding.
7. Which name most clearly communicates the role of a value representing the number of completed lessons?

   completedLessons communicates what the number represents. The other names reveal little or nothing about the program state.
8. Which line can read secret in this program? { const secret = "inside"; console.log(secret); }

   The binding is available inside its block, including the console.log statement there. It is not available after the closing brace merely because the block has finished.