Datatypes and variables

Data types

Though JavaScript is a weakly typed programming language, there are some data types between which JavaScript sometimes variables automatically converts:

null

Null means variable has no value at all. Do not confuse null with 0 (zero)! 0 is just a number, null means just no value or a empty or non-existent reference.

undefined

A value that is undefined is a value held by a variable right after it has been created and before a value has been assigned to it.