JavaScript: getSizeInContainer counting aspect ratio, x & y

static getSizeInContainer(item_x, item_y, container_x, container_y) {

        /* euclidean GCD (feel free to use any other) */
        function gcd(a, b) {
            if (b > a) {
                temp = a;
                a = b;
                b = temp
            }
            while (b != 0) {
                m = a % b;
                a = b;
                b = m;
            }
            return a;
        }

        /* ratio is to get the gcd and divide each component by the gcd, then return a string with the typical colon-separated value */
        function ratio(x, y) {
            c = gcd(x, y);

            var _x = (x / c);
            var _y = (y / c);

            return {
                x: _x,
                y: _y
            };
        }

        var item_aspect = ratio(item_x, item_y);

        if (!container_x) {
            // default value
            container_x = Dimensions.get('window').width * PixelRatio.get();
        }
        if (!container_y) {
            // default value
            container_y = Dimensions.get('window').height * PixelRatio.get();
        }

        var container_aspect = ratio(container_x, container_y);

        var new_item_x = null;
        var new_item_y = null;

        // which way (x or y) will be maxed
        if ((item_aspect.x / item_aspect.y) > (container_aspect.x / container_aspect.y)) {
            // x will be maxed and we will have some extra space on y axe
            new_item_x = container_x;
            new_item_y = (new_item_x * item_aspect.y) / item_aspect.x;

        } else {
            // y will be maxed and we will have some extra space on x axe
            new_item_y = container_y;
            new_item_x = (new_item_y * item_aspect.x) / item_aspect.y;
        }

        return {
            x: new_item_x,
            y: new_item_y,
        };

    }