When you use hexo s or hexo server and enabled it, it will run a websocket server(default port is 3000) and insert the javascript code to every page

npm i hexo-hotreload

in config.yaml

hotreload:
  enable: true
  port: 3007

If it's not working, try to refresh the page once again.

If it still not working, please try to restart the server or open an issue