Here is how you can write a simple “hello world” script using custom page for custom content box on any screen.
This example demonstrates how to call a sample .js page from the custom content box and give an alert “Hello World”.
Now you can write all your functions in this .js page that you intend to write in custom content. After following the above given steps you can see alert “Hello World” when the screen on which we have called the above page loads.