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Extensions overview

Ferrum extensions add things to the editor without changing the editor itself. An extension can:

  • add color themes and file icon themes
  • add languages, with their own syntax colors, comment markers and file types
  • add snippets that expand with the Tab key
  • add commands to the command palette and bind keyboard shortcuts to them
  • add settings that people can change
  • run JavaScript that reads and changes the open file, shows messages, panels and status bar items, and reacts to events such as saving a file

Extensions are shared through the Ferrum Marketplace, this site. People find them in the Extensions view inside the editor (the puzzle icon in the sidebar), read the description here or there, and press Install.

How it fits together

  1. You write an extension: a folder with a ferrum.json file (the manifest), and optional files such as a theme, a grammar, snippets and a JavaScript file.
  2. You run ferrum-ext package. It makes one file, name-1.0.0.fext, that holds everything.
  3. You publish the file on the marketplace: upload it on the Publish page, or run ferrum-ext publish.
  4. Anyone can install it from the editor. Ferrum downloads the .fext file, checks it, stores it on their computer and turns it on.

What Ferrum extensions are not

Ferrum is its own editor. Its extension system borrows ideas from VS Code, such as a manifest with contribution points and activation events, but VS Code extensions do not run in Ferrum. The API is different and smaller on purpose. Two things do carry over:

  • VS Code color themes work as they are. A contributes.themes entry can point at a VS Code theme file.
  • VS Code snippet files work as they are.

How code runs

An extension's JavaScript runs in a Web Worker, away from the editor's own code. It cannot touch the editor's page. It talks to the editor through the ferrum object, and every call that reaches outside the extension (reading a file, running a command, using the network) is checked against the permissions the extension declared and the user accepted at install time. Read Permissions and security before you publish code.

Extensions only run in a folder you have marked as trusted. In Restricted Mode only the passive parts (themes, snippets, languages, icon themes) are active; code does not run.

Where to go next

Your first extension →