How to write extensions

IMPORTANT: The extension location [changed] (https://github.com/adobe/brackets/wiki/New%20Extension%20Location) in Sprint 16

• [Download Brackets](How to Use Brackets#wiki-howtoget)
• Create a new folder in src/extensions/dev with yourExtensionName, and a main.js file for your extension code.
• For a quick start, you may want to read the Simple "Hello World" extension or refer to an existing extension (like InlineImageViewer) that is similar to what you want to do.
• If you're working on anything big we recommend you post to the brackets-dev Google group or the #brackets IRC channel on freenode early on so you can get feedback (there may be others working on similar ideas!).

Development Workflow:

• Open up Brackets, and if it's not already opened, open the brackets/ folder.
• Open a second window (Debug->New Window), which opens a new Brackets instance. You'll use this window for testing your extension. (This is optional: you can use just one window, but it's nice to have separate stable & testing windows in case you end up breaking Brackets in the process of developing your extension).
• In window #2, you can open a different folder on your file system to access other content for testing your extension (e.g. test.html).
• The development workflow is like this:
• In window #1, edit your extension code.
• In window #2, reload window (F5/Command-R) to get extension changes and test. Note: if your extension is not reloading correctly, disable caching in the Chrome Dev Tools
• To debug problems, open the developer tools for window #2 (Debug->Show Developer Tools). You can use console.log() from the extension code, set breakpoints, etc.
• Repeat.

Extension Architecture:

An extension consists of a main.js (your main module) and any other JS files (other modules). When you use Require in your main module to import your own modules, you get a private copy of modules, so they dont conflict with other modules. To access core Brackets modules, use brackets.getModule().

You often want an extension to integrate with the UI somehow. If your extension is doing something new from scratch, you can add new menu items or keyboard shortcuts for your new behavior -- see next section. Some Brackets features that already provide a UI are also extensible via feature-specific APIs -- see the section after next.

Adding menu items and keyboard shortcuts

See Simple "Hello World" extension for a code sample.

For any new behavior, first register a Command that implements your behavior, via CommandManager.register(). This just maps a Command id (string) to your handler function. Use package-style naming for your Command id (e.g. "myorg.myextension.mycommand") to avoid collisions with other extensions. (See also: [higher-level overview of command architecture](Brackets Development How Tos#wiki-commands)).

Add a menu item: Get a top-level menu by calling Menus.getMenu() with one of the AppMenuBar constants. Then add a menu item via theMenu.addMenuItem(), linking it to your Command id. The menu item's label will be the string name you gave the Command when it was created.

As a convenience, addMenuItem() also lets you create a keyboard shortcut for your Command at the same time.

Add a context menu item: Get a context menu by calling Menus.getContextMenu() with one of the ContextMenuIds constants (currently project-context-menu or editor-context-menu). Then add a menu item via theContextMenu.addMenuItem(), linking it to your Command id exactly like a top level menu item.

Add a menu divider Get a top level or context menu as explained above. Then add a menu dividers via theMenu.addMenuDivider(). It will default to the last position currently in the menu. You have the option of placing it with the position parameter first and last, which will place the divider accordingly. Additionally, you can set position parameter to before and after, pass in a Command ID, and place the divider accordingly.

Add a keyboard shortcut: To add a keyboard shortcut without any related menu item, call KeyBindingManager.addBinding() directly, linking a shortcut to your Command id. Be sure to use the Brackets Shortcuts page to see which shortcuts are available and to add the shortcuts that you use to the list.

To decline a keyboard event and allow other parts of Brackets to handle it, make your Command handler return a $.Promise that is already rejected at the time you return it. (This is useful if you want to override editing keys like Enter only when the cursor lies in certain places, and allow the default behavior in other cases; or always override a key in the code editor but allow default behavior in simpler textfields). (Note: requires Sprint 18 or later)

Adding new UI elements

Be sure to follow the Extension UI Guidelines.

Add UI elements to the DOM: Official APIs like the Quick Edit provider API above are the only officially supported way to add new UI elements to Brackets. You could just insert new DOM nodes somewhere, but it may break with future updates to Brackets.

Add a panel below the editor: There's no official way to do this yet, so you'll have to insert your own DOM elements. Tips:

• Be sure you add your panel above the status bar. To ensure this, use $myPanel.insertBefore("#status-bar") or better yet $myPanel.insertAfter(".bottom-panel:last").
• To make your panel resizable, use Resizer.makeResizable(): it even takes care of remembering the panels size across launches. See Resizer.js for documentation.

Load a CSS file: use ExtensionUtils.loadStyleSheet(). It returns a Promise you can use to track when the CSS is done loading.
To avoid accidentally breaking core Brackets UI, place a CSS class on the root of your UI and make sure all your CSS rules include a descendant selector. E.g. instead of li { ... } use .myExtension li { ... }.

Extending specific Brackets features

Quick Edit (inline editors): To create an extension that responds on CTRL+E (like the inline image viewer), use EditorManager.registerInlineEditProvider(). If multiple "providers" all want to respond in a given context, however, the first one wins - there's no notion of priority or cycling through providers yet.

Quick Open: To interface with the quick open (file open/jump to) feature, use QuickOpen.addQuickOpenPlugin().

Code Hints: To create an extension that shows a code hint popup, use CodeHintManager.registerHintProvider(). Unlike Quick Edit, these "providers" can have varying priority to resolve conflicts; more specific providers take precedence.

Syntax Coloring: Extensions can add new code-coloring "modes" via LanguageManager.defineLanguage(). See Language Support for details.

Accessing resources (e.g. images) in your extension

Extensions can get installed at (semi-)arbitrary paths. For example, you might develop your extension in the brackets/src/extensions/dev/foo directory, but a user might install it in /Users/<user>/Library/Application Settings/Brackets/extensions/user/bar.

Thankfully, the require context that's passed in to your extension's main.js file can help you resolve paths. Just call require.toUrl with the relative (to your module) path you'd like to make relative to the site root. IMPORTANT: Make sure you're using the require object that was passed to your module, not the global require object.

For example, if you have awesome.jpg in your extension's top-level foo folder, you can do require.toUrl('./awesome.jpg'), and it will return something like /extensions/dev/foo/awesome.jpg when you call it and /Users/<user>/Library/Application Settings/Brackets/extensions/user/bar/awesome.jpg when your user calls it. The path you give toUrl should be relative to your extension's top-level folder (yes, subdirectories work), and the URL you get back will be relative to the site root (i.e. it will begin with "/").

Further reading

For more detail on Brackets internals, see Brackets Development How Tos.

If you're interested in contributing to the core Brackets codebase, see How to Hack on Brackets.