Undefined variable: A variable which is declared but value is not defined for that.
Undefined value: A value that is not defined and has no keyword is known as undefined value.
var testNum; console.log(testNum); // undefined
Note: Undefined is of the type undefined.
var testNum; console.log(typeof testNum); // undefined
Null value: A value that is explicitly specified by the keyword “null” is known as null value.
var test= null; console.log(test); // null
Note: null is of the type Object.
var test= null; console.log(typeof test); // object