When I was starting in Web development I was coding client side validation in pure JavaScript, after that I started using jQuery, and finally I discovered Parsley.js. Every time my motivation to move from one option to another was amount of code I need to write, and how easy it was to maintain that code. With Parsley everything is so easy, and because it uses inline syntax, it is easier to follow validation logic. There are no JS functions for email format validation, I don’t need to take care about email format, domain etc. Also I don’t need to write password confirmation logic, nor any other usual function, everything is built-in.

Few times I needed some custom validation logic involving checkboxes, and one validation flow if it is checked, and other if not, and I extended Parsley with custom validator in few lines. So if you need client side form validation library, look no more, you found it.