Empty / Undefined / Null in JavaScript

In this article, we will learn the concept of empty, undefined and null in JavaScript and how to use JavaScript to check the Empty, Null and Undefined string on the client/user side for authentication purpose.

This is functional to have accurate and consistent data before forwarding it to the server. We can assume that the main purpose of this function is to validate the values input by the users either empty or filled.

In formal language theory, the empty string, or empty word, is the unique st...