What can libraries do
If you create Google Apps libraries, you can use them from the external environment.
Here is the way how to create Google Apps Script libraries.
If you want to know how to use libraries, please refer the following page:
Step 1. Create a library
Go to “File” -> “Manage versions
Click a button “Save new version”. If you want to save an explanation, please enter something in a text box
The library is saved then you can see like the following image.
Step 2. Share your library with others
Go to “File” -> “Share”.
Edit the sharing information.
Note: How to not allow to use a library by others
Please add “_” on the end of a function name you don’t want to allow to use it by others.