What’s the difference between null, undefined and NaN in JavaScript?

null

A null value represents nothing, nonexistent or invalid object or address. It converts to 0 in simple arithmetic operations and it’s global object. null == false gives us false.

undefined

The global undefined property represents the primitive value undefined. It tells us something has not assigned value; isn’t defined. undefined isn’t converted into any number, so using it in maths calculations returns NaN.

NaN

NaN (Not-A-Number) represents something which is not a number, even though it’s actually a number. It’s not equal to itself and to check if something is NaN we need to use isNaN() function.