Null - MDN Web Docs Glossary: Definitions of Web-related terms 编辑

In computer science, a null value represents a reference that points, generally intentionally, to a nonexistent or invalid object or address. The meaning of a null reference varies among language implementations.

In JavaScript, null is marked as one of the primitive values, because its behaviour is seemingly primitive.

But in certain cases, null is not as "primitive" as it first seems! Every Object is derived from null value, and therefore typeof operator returns object for it:

typeof null === 'object' // true