JavaScript Scope, Environments, and Closures Quiz

Review

1. Which binding does an identifier normally use first?

   Name resolution starts in the current lexical environment and follows outer environments only when necessary.
2. What does shadowing mean?

   An inner binding with the same name is selected for references within its scope.
3. Why is JavaScript described as lexically scoped?

   The nesting where a function is defined determines the environments it can use for name resolution.
4. What is the key property of a closure?

   A closure preserves access to the lexical environment used by the function.
5. Two closures returned from the same factory can observe the same mutable binding. Why?

   Both functions can close over the same binding created by the factory invocation.
6. Why can for (let i = 0; i < 3; i++) closures produce 0, 1, 2?

   let in a for-loop has per-iteration behavior that allows closures to retain the corresponding iteration binding.
7. A callback reads prefix defined in the function that created it. What mechanism makes this work?

   The callback closes over the lexical environment where it was created.
8. A function is called from a scope containing a local name x, but x was not in the function’s defining scope. Can that caller local x become visible just because of the call?

   Calling a function from another scope does not replace its lexical environment.
9. What happens when identifier lookup reaches the end of the environment chain without finding a binding?

   An unresolved identifier reference produces a ReferenceError during evaluation.
10. What is resolved first in user.name?

    The user identifier must be resolved before the name property can be accessed on its value.