FrontendHaltTypeScript·Intermediate·Coding·1 min read
Why does typeof null equal object, and how should code narrow it?
Short interview answer
That result is a historical JavaScript behavior. Check value !== null before treating an object-typed value as an object, because a typeof value === 'object' branch otherwise includes null.
Example
function keys(x: object | null) { if (typeof x === 'object' && x !== null) { return Object.keys(x); // without the null check, x could be null } return [];}Key takeaway
Explain the underlying mental model clearly, then support it with a concrete example and its trade-offs.