In English, null means nothing, but in JavaScript, that nothing can become a headache. Let's overthink it and try to understand why and how.
As per MDN,
In JavaScript, a primitive (primitive value, primitive data type) is data that is not an object and has no methods or properties.
Since null is one of the 7 primitive data types, it is not an object.
What about typeof null? It returns the string "object".
Well, though null is a primitive data type, typeof null is not. typeof null is just a string, the result of using typeof, which is a way to check the type of any value. And typeof null === "object" is nothing but a bug that was left unsolved intentionally, so old websites wouldn't break.
So what about typeof Number, typeof String etc. returning "function"?
That's a different thing, and it's called a constructor). By convention, a constructor starts with a capital letter, and it is completely different from the same name with a lowercase letter because JavaScript is case-sensitive. So, "number" is completely different from Number. One is the type label typeof returns for values like 5, and the other is a constructor function.
So why does typeof Null/Undefined return "undefined"?
It's easy to mix things up as a beginner, but there is no such thing in JavaScript as Null or Undefined with a capital N/U. They are undeclared names, and typeof doesn't throw an error on undeclared names.
typeof Null; // "undefined" (undeclared name; typeof doesn't throw)
Null; // ReferenceError: Null is not defined
Separately, null & undefined have no constructor function or wrapper object. That's also why property access on them fails instead of autoboxing:
null.toString(); // TypeError
undefined.toString(); // TypeError
So what did we learn from this article? Literally nothing aka null.