Yes require.js, i have a work around which is the below, which does the same thing and works but just isnt as tidy or compact, the only problem is that in manually reversing the initial tween (using x, y position) the reversal in the second tween takes place from the end point of the first tween animation and not from the current position of the first tween at the point of mouseleave
define(['jquery', 'TweenLite', 'TimelineLite', 'gsapCss', 'gsapJquery'], function ($) { 'use strict';});
var $div_1 = ('.div_1')
var $element_2 = ('.element_2');
$('.div_1').mouseenter(function(){
console.log("runs");
TweenLite.fromTo($element_2, 1, {x:0, ease:Power4.easeIn }, {x:-150, ease:Power2.easeOut});
});
$('.div_1').mouseleave(function(){
console.log("runs");
TweenLite.fromTo($element_2, 1.5, {x:-150, ease:Power2.easeIn }, {x:0, ease:Power4.easeOut });
});