[Solved] why do developers prefer JavaScript for form validation, if it can be possible from HTML5? [closed]

From tutorialspoint:
Form validation normally used to occur at the server, after the client had entered all the necessary data and then pressed the Submit button. If the data entered by a client was incorrect or was simply missing, the server would have to send all the data back to the client and request that the form be resubmitted with correct information. This was really a lengthy process which used to put a lot of burden on the server.

JavaScript provides a way to validate form’s data on the client’s computer before sending it to the web server. Form validation generally performs two functions.

Basic Validation − First of all, the form must be checked to make sure all the mandatory fields are filled in. It would require just a loop through each field in the form and check for data.

Data Format Validation − Secondly, the data that is entered must be checked for correct form and value. Your code must include appropriate logic to test correctness of data.

This makes sense because sending data back and forth from the server can be intensive. Also, if you use HTML5 to validate, you are most likely going to run into people who don’t use HTML5 compliant browsers, and will avoid your validation technique. You could develop two pages, one that is for html5 complient browsers, and one that detects and displays a non html5 page with javascript to valideate.

https://www.tutorialspoint.com/javascript/javascript_form_validations.htm