Finally I know the reason. I used Chrome browser for debugging. It does not support cross-domain requests, that is, it does not support routing. After I changed to Firefox, it ran normally. For details on how to solve the problem using Chrome, see the link http:/ /jingyan.baidu.com/article/7c6fb4281d685780642c900a.html But my attempt was unsuccessful
Finally I know the reason. I used Chrome browser for debugging. It does not support cross-domain requests, that is, it does not support routing. After I changed to Firefox, it ran normally. For details on how to solve the problem using Chrome, see the link http:/ /jingyan.baidu.com/article/7c6fb4281d685780642c900a.html
But my attempt was unsuccessful