jtree has three admin interfaces, each a folder in client/internal/clients/admin/, served at /admin/<folder>/. They need no build step: jtree serves the folder as it is, and the page compiles its Vue and TypeScript files in the browser. Edit a file and reload the page.
v2/: jtree's admin, also served at/admin/(the settingdefaultAdminUI). See itsREADME.md.ztree/: the z-Tree admin. See itsREADME.md.otree/: the oTree admin. See itsREADME.md.multiuser/: the previous admin.
An admin talks to the server over socket.io messages (server/source/core/Msgs.js), and its editors over the editor API (/api/editor/…, server/source/editors/). Another folder in client/internal/clients/admin/ is served the same way, so an admin of your own can sit beside these.