jq判斷觸屏左右滑動方向

$('body').on('touchstart', '.slide-box>ul>li', function(e) {
    var touch = e.originalEvent,
        startX = touch.changedTouches[0].pageX;

    $(this).on('touchmove', function(e) {
        e.preventDefault();
        touch = e.originalEvent.touches[0] ||
            e.originalEvent.changedTouches[0];
        if (touch.pageX - startX > 20) {//向左
            $('#preBtn').click();
            $(this).off('touchmove');

        } else if (touch.pageX - startX < -20) {//向右

            $('#nextBtn').click();

            $(this).off('touchmove');

        };

    });

    // Return false to prevent image
    // highlighting on Android
    //return false;

}).on('touchend', function() {
    $(this).off('touchmove');
});