Form validation ensures that the user submits the correct data and is made aware of any incorrect input data. Form validation involves identifying what type of input the form fields require and then checking the contents of each form field. Once an incorrect data item is detected, the user is notified, typically through an error message and the highlighting of the incorrectly completed input box.
Note
Note that a web application should never rely on just client-side data validation. Since client-side data validation can be easily circumvented by a malicious user, data validation should always be handled server-side. Only through server-side data validation can you ensure the security of your web application.
As form validation is a well-explored area within web development, we luckily do not need to implement all of the aforementioned from scratch. There exist plenty of third-party libraries that allow one to implement data validation quickly and with relatively little effort...