easeInOutElastic (t) {
        const s = 0.1125;
        const p = 0.45;
        return atEdge(t) ? t : t < 0.5 ? 0.5 * elasticIn(t * 2, s, p) : 0.5 + 0.5 * elasticOut(t * 2 - 1, s, p);
    }
Easing functions adapted from Robert Penner's easing equations.
@namespace Chart.helpers.easing.effects
@see http://www.robertpenner.com/easing/