wx.createSelectorQuery().select(`#${canvasId}`).fields({
  node: true,
  size: true,
}).exec(async (resList) => {
  if (!resList.length) return;  

  const { node: canvas } = resList[0];
  const ctx = canvas.getContext('2d')!;
  console.log(ctx.canvas === canvas); // 返回 false，期望是 true
});
// 此处实现跟标准不同，所以封装自定义逻辑函数，需要同时传 ctx 和 canvas...