What is form validation in JavaScript? How client side validation is different from server level validation. 

Question :

What is form validation in JavaScript? How client side validation is different from server level validation. 

Whenever we are working with Forms on webpages to submit some data, the Form validations are usually occurring at the server end, i.e. as the user entered all the necessary data and press the Submit button, all the filled data are submitted to server and subsequently validated. If the data entered by the user is incorrect or simply missing, the server sends all the data back to the client and requests for resubmitting of data through form with correct information. This is really a lengthy process which used to put a lot of burden on the server.

Using JavaScript, there are ways to validate most of the form's data on the user system itself before sending it to the web server. This is called Form validation and generally performs two functions:

Basic Form Validation – In this, initially form must be checked to make sure all the mandatory fields are filled in. This is simple and requires a loop through each field in the form to check for data. For Example, Name, Mobile no. and email is mandatory. 

Data Format Validation – In this type of validation, the data entered can be checked for correct format and values (may be some value ranges). It is required that the JS code written must include appropriate logic to test correctness of data. For example, mobile no must be of 10 digits, email must be in correct format or PinCode shall be of 6 digits not starting with zero or Marks obtained shall be between 0 and 100.