在安卓系统中正常运行  canvas.toDataURL() 方法在iphone11 pro 中返回值为字符串“data:,” 下面代码中end()方法中无法转canvas为 二进制base64

methods: {  
    init(res) {
      const width = res[0].width
      const height = res[0].height
      canvas = res[0].node
      //获得Canvas的上下文
      context = canvas.getContext('2d')
      dpr = wx.getSystemInfoSync().pixelRatio
      canvas.width = width * dpr
      canvas.height = height * dpr
      context.scale(dpr, dpr)
      context.strokeStyle = "#000";
      context.lineWidth = 3;
      //设置线两端端点样式更加圆润
      context.lineCap = 'round';
      context.lineJoin = 'round';
      context.fillStyle = "#ffffff"
      context.fillRect(0, 0, canvas.width, canvas.height);
    },
     // 画布的触摸移动结束手势响应
    end: function (e) {
      console.log("触摸结束", e);
      //清空轨迹数组
      for (let i = 0; i < touchs.length; i++) {
        touchs.pop();
      }
      // 保存当前绘图数据到数组中，撤销的时候能用得上
      if(imgList.length>=10){
        imgList.pop()
      }
      if(this.data.isdraw) {
        imgList.push(canvas.toDataURL());
      }
      if(imgList.length >=1) {
        this.setData({ disableSign: false });
        this.data.isdraw = false;
      }
    },
};