Doesn't update automatically when i change any code in custom app

For example, if i change my custom script code in custom_app js file. But when i reload the desk, the updated code doesn’t show in console panel. Previous output was shown.
So i need to stop the server and again start the server. Then i can see my updated code output.

It also happened when i working backend code python.

Why this problem happened:
OS: Ubuntu 18.04