Compose a module and inspect its manifest

Before you start: complete Start the local backend lab, or make sure you can pass its checkpoint.

Give one module one capability#

The backend lab has a module named learn_api. Its model key is learn_api.Todo, and its operations are learn_api.list, learn_api.create and learn_api.complete. Those names are public contracts inside the composed application.

Open modules/learn_api.ts in the downloaded lab. Follow its sections in order: models describe data, functions describe behavior, and messages hold translated text. The module does not open a database or listen on a port when imported.

Inspect before serving#

# Run from: learn_api
npm run build
npx ket check --workspace dist/ket.workspace.js
npx ket manifest --deployment learn_api --workspace dist/ket.workspace.js
npx ket modules --workspace dist/ket.workspace.js

Find the Todo fields and the three functions in the manifest output. Inspect each function's effects. This is the composed contract used by the application, not an independently maintained document.

Try a composition error#

In a scratch copy, give a second module the same module name and include both in the deployment. Run ket check. Read the error, then undo the change. Repeat with an unresolved declared dependency. These failures should occur while composing the application, before a request reaches a handler.

When one module extends or references another module's contribution, declare the dependency explicitly. A file import and a manifest dependency are different things: the former loads code; the latter records the relationship the framework checks.

Explore module discovery#

The small lab imports its module directly. Larger workspaces may resolve modules from declared roots. Use ket modules to see the resolved sources and learn the root configuration before relying on filesystem discovery. Do not scan an arbitrary installed directory and treat every file as enabled functionality.

Make a small extension#

Add a translated message for the task list title and run check again. Then compare the manifest before and after. The goal is to see how a small source contribution changes the application contract.

Checkpoint#

The manifest contains your module once, with the expected Todo model and function effects. An intentional composition conflict fails check.

Practice on your own#

Sketch a second module for reminders. Identify which contributions it owns and which dependency it would declare on the Todo module.

Reference#

For the complete API contract, read Modules.