Answer 1

Question is Not clear to me...
If you mean if condition to make false when true you can use not(!) opearor..
if( !(condition))

Answer 2

Where you start your animation that can be assigned to a variable. And leter this animation can be canceled such as:
var reqaf = requestAnimationFrame(animate);
// other code .....
if(isInView(item))
cancelAnimationFrame(reqaf);

Here is a live example for it:

https://code.sololearn.com/WJqv5tPfKuso/?ref=app