easing

u.ease = {
        quadratic: {
            style: 'cubic-bezier(0.25, 0.46, 0.45, 0.94)',
            fn: function (k) {
                return k * ( 2 - k );
            }
        },
        circular: {
            style: 'cubic-bezier(0.1, 0.57, 0.1, 1)',   // Not properly "circular" but this looks better, it should be (0.075, 0.82, 0.165, 1)
            fn: function (k) {
                return Math.sqrt( 1 - ( --k * k ) );
            }
        },
        back: {
            style: 'cubic-bezier(0.175, 0.885, 0.32, 1.275)',
            fn: function (k) {
                var b = 4;
                return ( k = k - 1 ) * k * ( ( b + 1 ) * k + b ) + 1;
            }
        },
        bounce: {
            style: '',
            fn: function (k) {
                if ( ( k /= 1 ) < ( 1 / 2.75 ) ) {
                    return 7.5625 * k * k;
                } else if ( k < ( 2 / 2.75 ) ) {
                    return 7.5625 * ( k -= ( 1.5 / 2.75 ) ) * k + 0.75;
                } else if ( k < ( 2.5 / 2.75 ) ) {
                    return 7.5625 * ( k -= ( 2.25 / 2.75 ) ) * k + 0.9375;
                } else {
                    return 7.5625 * ( k -= ( 2.625 / 2.75 ) ) * k + 0.984375;
                }
            }
        },
        elastic: {
            style: '',
            fn: function (k) {
                var f = 0.22,
                    e = 0.4;

                if ( k === 0 ) { return 0; }
                if ( k === 1 ) { return 1; }

                return ( e * Math.pow( 2, - 10 * k ) * Math.sin( ( k - f / 4 ) * ( 2 * Math.PI ) / f ) + 1 );
            }
        }
    }