Explain few difference between null, undefined or undeclared JavaScript variable?

Answer:

Null:- Null is a value that can be assigned to a variable or an object.

Undefined:-Undefined means a variable has been declared but no value is assigned to it. This type of variable is declared itself to be undefined.

Undeclared:-Undeclared means the variable has declared without any datatype.

Null, Undefined are primitive data types whereas Undeclared is not a primitive data type.