onLoad: function () {
   this.setData({
     height: wx.getSystemInfoSync().windowHeight,
     width: wx.getSystemInfoSync().windowWidth
   })
 }

.index{
   height: 100vh;
   width: 100vw;
}
# CSS3引入的"vw"和"vh"基于宽度/高度相对于窗口大小 
# "vw" = "view width"  "vh" = "view height"