var winWidth = 0 
var winHeight = 0 
var diameter = 10 
var time = 0 
Page({ 
 data:{ 
  numX:1, 
  numY:1 
 }, 
 xy:{ 
  //小球的xy坐标 
  x:10, 
  y:10 
 }, 
 onLoad:function(options){ 
  //进来先获取手机的屏幕宽度和高度 
  wx.getSystemInfo({ 
   success: function(res) { 
    console.log(res) 
    winHeight = res.windowHeight; 
    winWidth = res.windowWidth; 
   } 
  }) 
 }, 
 onReady:function(){ 
   //循环滚动小球 
   for(var i=0;i<1;i++){ 
    //随机一个滚动的速度 
    time = (1+Math.random()*10) 
    setInterval(this.move,time); 
    console.log(time) 
   } 
 }, 
 move(){ 
  //x  
  if(this.data.numX == 1){ 
   this.xy.x++ 
  }else{ 
   this.xy.x-- 
  } 
  //判断x轴的状态 
  if(this.xy.x == winWidth-diameter){ 
    this.data.numX=2 
  } 
  if(this.xy.x == diameter){ 
    this.data.numX=1 
  } 
  //y 
  if(this.data.numY == 1){ 
    this.xy.y++ 
  }else{ 
    this.xy.y-- 
  } 
  //判断y轴的状态 
  if(this.xy.y == 400-diameter){ 
    this.data.numY=2 
  } 
  if(this.xy.y == diameter){ 
    this.data.numY=1 
  } 
  //画图 
  this.ballMove(this.xy.x,this.xy.y); 
 }, 
 ballMove(x,y){ 
  // 使用 wx.createContext 获取绘图上下文 context 
  var context = wx.createContext() 
  // context.setShadow(0,1,6,'#000000')//阴影效果 
  context.setFillStyle("#FF4500")//球的颜色 
  context.setLineWidth(2) 
  context.arc(x, y, diameter, 0, 2 * Math.PI, true) 
  context.fill() 
  // 调用 wx.drawCanvas，通过 canvasId 指定在哪张画布上绘制，通过 actions 指定绘制行为 
  wx.drawCanvas({ 
   canvasId: 'ball', 
   actions: context.getActions() // 获取绘图动作数组 
  }) 
 } 
}) 

   canvas-id="ball">