var that = this;
    wx.getSystemInfo({
      success:function(res){
        var width = res.windowWidth
        wx.getImageInfo({
          src: “…/…/images/index.png”,
          success: function (res) {
            var height = res.height*width/res.width
            console.log(res);
            that.setData({
              width: width,
              height: height
            });
          },
          complete: function(res){
            console.log(res);
          }
        })
      }
    });