client side gravity form validation

How can I perform Client Side Form validation (to perform form's onSubmit, or submit's button onClick).
I know that there is a way to perform a custom validation at server side with gform_field_validation, but I want to perform a validation with JavaScript before going to Server Side, so that page won't be reloaded.
Another question , in case there is a way to perform JavaScript validation on Form's Submit - what is the best way to get form's fields, with stars ( mandatory fields ), at my Client Side script.