App Backend

The backend is a Node app under app-backend/. You implement business logic; the Appnest stack loads server.js, wires routing, and exposes your exports to the platform.

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Entry point: app-backend/server.js

• Only functions exported from server.js can be invoked by the platform (backend API calls, event handlers, scheduled work—per your manifest.json).
• Register API surfaces under backend_api_functions and event handlers under event_listener_functions (each handler must match an export name). Full schema: Manifest.

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AppnestFunctions for backend code

Need	Module	Doc
Outbound HTTP	$fetch	External API
Key/value storage	$db	Data Storage
Files (signed URLs, list, delete, …)	$file	File Storage
Scheduling	$schedule	Schedule
Call another backend function	$next	Background Job

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How to code

• Use CommonJS only: require / module.exports. Do not use import / export / import() in app-backend (the validate command enforces this).
• Keep export names identical to keys in manifest.json so validation passes.

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Rules

• Manifest alignment: Every backend_api_functions key and every event handler must exist as a real export on server.js.
• Validation: Run appnest-development-engine app validate before commits or in CI (lint + manifest checks).
• Unused catch binding: If you do not use the error, use a parameterless catch { } (not catch (e) with an unused e).

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Returning data to the frontend

When the UI invokes a backend function, the client typically receives an object shaped like { statusCode, body }: statusCode is an HTTP-style code (e.g. 200, 400, 401); body is what the function returned. If your backend uses a ResultData({ body, statusCode }) (or equivalent) helper, those values flow through to the client; otherwise the framework may default statusCode (e.g. 200) and put a plain return value in body. Exact behavior can depend on your app template—test against your scaffold.

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Local dev note

Under the dev proxy, backend traffic is usually available under paths such as /app-backend/.... You do not run a separate public HTTP server for normal Appnest local development.

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Further reading (this site)

Topic	Document
App shape & project layout	App Overview
Manifest schema & installation_parameters	Manifest
Appnest Functions	Appnest Functions overview
Engine & CLI	Development Engine overview, Commands