Omitting the parameter returns the current value (getter), whereas defining the parameter sets the value (setter) and returns the instance itself for easier chaining.
GreenSock Docs (HTML5/JS)
TweenLite
.reversed()
Gets or sets the animation's reversed state which indicates whether or not the animation should be played backwards.
Parameters
value: Boolean
(default = false
) — Omitting the parameter returns the current value (getter), whereas defining the parameter sets the value (setter) and returns the instance itself for easier chaining.
Returns : *

Details
Gets or sets the animation's reversed state which indicates whether or not the animation should be played backwards. This value is not affected byyoyo
repeats (TweenMax and TimelineMax only) and it does not take into account the reversed state of anscestor timelines. So for example, a tween that is not reversed might appear reversed if its parent timeline (or any ancenstor timeline) is reversed.
This method serves as both a getter and setter. Omitting the parameter returns the current value (getter), whereas defining the parameter sets the value (setter) and returns the instance itself for easier chaining.
var rev = myAnimation.reversed(); //gets current orientation
myAnimation.reversed( true ); //sets the orientation to reversed
myAnimation.reversed( !myAnimation.reversed() ); //toggles the orientation