What are null and undefined, and what is the difference? What will typeof null return?

null and undefined are two different types in JavaScript that denote the absence of a value but are used in different situations:

• undefined means that a variable is declared but not assigned a value.
• null is an explicit assignment of the value "empty" or "no object".

Difference:

• undefined is the default type for undeclared or uninitialized variables.
• null is an object that a programmer can assign to a variable to indicate the absence of a value.

What does typeof null return?

console.log(typeof null); // "object"

This is a historical quirk of JavaScript: null is considered an object, although by its nature it is a primitive representing an empty value.