JavaScript Symbols and Property Protocols Quiz

Review

1. Which statement about Symbol() is correct?

   The description is not identity; each Symbol() call creates a distinct Symbol value.
2. Which values can be object property keys?

   ECMAScript property keys are Strings or Symbols.
3. How do you access a property whose key is stored in symbolKey?

   Bracket notation with the Symbol value uses that exact Symbol as the key.
4. Which API returns all own property keys, including Symbols?

   Reflect.ownKeys returns both String and Symbol own keys.
5. What is special about Symbol.for("x")?

   Symbol.for uses the global Symbol registry, so the same key retrieves the same registered Symbol.
6. What does Symbol.keyFor return for a registered Symbol?

   Symbol.keyFor returns the string used to register the Symbol, or undefined for an unregistered Symbol.
7. What are well-known Symbols primarily used for?

   ECMAScript defines well-known Symbols as extension points used by specified algorithms.
8. Which hook connects an object to synchronous iteration?

   for...of obtains an iterator through Symbol.iterator.
9. Which hook is preferred by for await...of when present?

   for await...of first looks for Symbol.asyncIterator.
10. What must Symbol.toPrimitive return?

    The conversion hook must return a primitive; otherwise the operation throws.
11. What does Symbol.toStringTag influence?

    Object.prototype.toString consults Symbol.toStringTag for the descriptive brand.
12. Which operator can consult Symbol.hasInstance?

    instanceof can use the constructor’s Symbol.hasInstance method.
13. Which method consults Symbol.isConcatSpreadable?

    concat checks Symbol.isConcatSpreadable when deciding whether to spread an object.
14. Which string operation consults Symbol.match on its argument?

    String.prototype.match invokes the Symbol.match method of its argument when available.
15. Which comparison is true?

    Repeated Symbol.for calls with the same key return the same registered Symbol.
16. Which mental model best describes a standardized Symbol protocol?

    The operation defines which Symbol-keyed property it consults and what that hook must do.