The green sign-in button is displayed and hidden according to the current system time. For example, the class time of physical education class is 11:15, then the display time period of the sign-in button should be 10:45-11:15, and it will not be displayed at other times. Now I performed a local test by modifying the system time and found that I could not get real-time results. I had to refresh the browser multiple times and clear the cache and temporary files. What is the problem? 
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
Written by AJAX? The page displays a certain element and JS judgment is enough. As for the problem of multiple refreshes you mentioned, you can just change the browser and test it.