Open VSCode. Go to extensions and search for "ObjectScript" like it is shown on the attached screenshot and install it.
Or install from ObjectScript extension page on Visual Studio Marketplace
To be able to use many plugin features, you need to configure the connection to Caché server first.
Find a 'objectscript.conn' section in workspace settings (File - Preferences - Settings), do not forget to set active to trueport should follow to web port of instance (usually by default, 57772 for Caché/Ensemble, 52773 for IRIS)