What are the quirks of the typeof operator?

Question presented to candidate: "If a variable was genuinely never declared anywhere, does typeof someUndeclaredVar throw an error? What if you just wrote someUndeclaredVar directly, without typeof — same answer?"

What a strong answer should cover:

• 📌 Interview term: the real, direct answer to the prompt — verified directly: typeof on a genuinely undeclared variable does NOT throw at all — it genuinely returns the string "undefined". A bare reference to that SAME undeclared variable, without typeof, genuinely DOES throw a real ReferenceError — typeof is a real, deliberate special case, safely checking for a variable's existence without risking a crash.
• 📌 Interview term: typeof null is "object" — a famous, real historical bug, preserved for backward compatibility — covered in more depth in this bank's own dedicated null-vs-undefined question.
• 📌 Interview term: typeof on arrays and NaN — verified directly: typeof [] is genuinely "object", not a separate "array" category (Array.isArray() is the correct, dedicated check); typeof NaN is genuinely "number", since NaN is a real, valid (if invalid-representing) member of the Number type.
• 📌 Interview term: functions are the one real exception — verified directly: typeof on a function (including a class, which is genuinely a function under the hood) returns "function" — the ONE value typeof can return that does not correspond to one of the七 formal ECMAScript language types directly, a real, deliberate special case for a callable value.
• A precise answer names typeof genuinely returning a real result for every one of the primitive types plus "object"/"function"/"undefined" — Symbol() genuinely returns "symbol", and a BigInt literal genuinely returns "bigint" — verified directly, confirming typeof stays accurate for every newer primitive type added to the language too.

Clarifying questions expected:

• None — this is a definitional/technical question; directly answering the prompt's own undeclared-variable scenario (typeof vs. bare reference) is the strong signal, since it is the single most useful, commonly-missed typeof quirk.

Code / implementation expected: Yes — the direct side-by-side typeof undeclaredVar vs. a bare undeclaredVar reference is the clearest, most convincing demonstration.