Coding Plugin
Develop a plugin. Follow the plugin structure described here.
Write code for each plugin type using the corresponding variables, methods and items. Put the scripts into the src folder. Specify the required Plugin interface for each plugin to be embedded in the portal.
Specify plugin messages that will be returned by the items. Use the appropriate events that will be processed on the portal side.
Learn which plugin components can be used for the DocSpace plugin interface and add them to your scripts.
Code samples are available at https://github.com/ONLYOFFICE/docspace-plugins.