长按保存图片，或点击按钮保存

 $("#savebtn").on({
        touchstart: function (e) {
            // 长按事件触发
            timeoutevent = settimeout(function () {
                timeoutevent = 0;
                save();
            }, 400);
            //长按400毫秒
            // e.preventdefault();
        },
        touchmove: function () {
            cleartimeout(timeoutevent);
            timeoutevent = 0;
        },
        touchend: function () {
            cleartimeout(timeoutevent);
            if (timeoutevent != 0) {
            }
            return false;
        }
    })
    function save()
    {
        

$.ajax({
            url: '****',
            type: 'post',
            data: { typecode: typecode },
            contenttype: 'application/json',
            success: function (data) {
                var a = $("<a></a>").attr("href", "data:image/png;base64," + data.data.image).attr("download", "***.png").appendto("body");
                a[0].click();
                a.remove();
            }
        });
    }