<canvas type="2d" id="myCanvas"></canvas>

 Page({
  onReady() {
    const query = wx.createSelectorQuery()
    query.select('#myCanvas')
      .fields({ node: true, size: true })
      .exec((res) => {
        const canvas = res[0].node
        const ctx = canvas.getContext('2d')

        const dpr = wx.getSystemInfoSync().pixelRatio
        canvas.width = res[0].width * dpr
        canvas.height = res[0].height * dpr
        ctx.scale(dpr, dpr)

        ctx.fillRect(0, 0, 100, 100)
      })
  }
})
z针对于这种生成canvas的方式，canvas的标识为id，那么
 wx.canvasToTempFilePath({
  canvasId: "mycanvas",
  success: function(res) {
   var tempFilePath = res.tempFilePath;
    that.setData({
     loadImagePath: tempFilePath,
     });
  },
   fail: function(res) {
       console.log(res);
   }
  });
wx.canvasToTempFilePath将canvas生成为图片是根据canvasId，也就导致wx.canvasToTempFilePath获取不到canvas。这怎么办。

xin.qq.com/miniprogram/dev/component/canvas.html