Architecture Overview

This section describes the overall architecture of Theia.

Theia is designed to work as a native desktop application as well as in the context of a browser and a remote server. To support both situations with a single source, Theia runs in two separate processes. Those processes are called frontend and backend respectively, and they communicate through JSON-RPC messages over WebSockets or REST APIs over HTTP. In the case of Electron, the backend, as well as the frontend, run locally, while in a remote context the backend would run on a remote host.

Both the frontend and backend processes have their dependency injection (DI) container (see below) to which extensions can contribute.


The frontend process represents the client and renders the UI. In the browser, it simply runs in the rendering loop, while in Electron it runs in an Electron Window, which basically is a browser with additional Electron and Node.js APIs. Therefore, any frontend code may assume browser as a platform but not Node.js.

The startup of the frontend process will first load the DI modules of all contributing extensions before it obtains an instance of FrontendApplication and call start() on it.


The backend process runs on Node.js. We use express as the HTTP server. It may not use any code that requires a browser (DOM API) as the platform.

The startup of the backend application will first load the DI modules of all contributing extensions before it obtains an instance of BackendApplication and calls start(portNumber) on it.

By default the backend's express server also serves the code for the frontend.

Separation By Platform

In an extension's top folder we have an additional layer of folders to separate by platform:

  • The common folder contains code that doesn't depend on any runtime.
  • The browser folder contains code requiring a modern browser as a platform (DOM API).
  • The electron-browser folder contains frontend code that requires DOM API as well as Electron renderer-process specific APIs.
  • The node folder contains (backend) code requiring Node.js as a platform.
  • The node-electron folder contains (backend) code specific for Electron.

See also

For a high level overview of Theia's Architecture, see this document:

Multi-Language IDE Implemented in JS - Scope and Architecture

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