Form validation with javascript

Question

Hi
I designed a registration form
I used javascript to make the mobile number validation.
Is it enough or maybe hacked by the browser?

Answer 1

When you set the onclick event listener to the submit button, it send you an argument, you can use that to prevent redirection, get the value of inputs and check that:

https://code.sololearn.com/WT4cnRoeLq6t/?ref=app

Answer 2

I mean, if I do validation with javascript, is it okay for my security? Not hacked?