You can write small microservices inside the editor microservices Code Tab. It is not a full-featured IDE, but you can create some basic field resolvers there and bind them to serverless functions. It is definitely enough to, for example, write integration code.
Currently microservices can be written in TypeScript and JavaScript. Our editor also supports package.json and tsconfig.json out of the box. If you have a build script you should provide it during deployment inside the popup dropdown menu.