Add class on scroll into viewport

Is it possible to be able to add a class to an object when scrolled into the viewport so we could use CSS to apply animations and/or transitions? If we could create our own class names and create associated CSS to that class to create our own special effects. This is possible with JQuery but I'm trying not to use that. I'd also like to be able to define the percentage of the object in view before adding the class. (hoping)