Implement method-specific exports for API handlers

[Copilot]

Adds support for method-specific exports in API handlers, allowing developers to use named exports like export const GET = (req, res) => {...} in addition to the legacy default export pattern.

Changes

Core Implementation

• Updated adex/runtime/handler.js: Added getMethodHandler() function that implements method-specific dispatch logic with proper fallback behavior
• Updated adex/src/http.d.ts: Added TypeScript types for APIHandler and APIModule interface supporting both export patterns

Key Features

• ✅ Method-specific exports: Support for GET, POST, PUT, PATCH, DELETE, OPTIONS, HEAD
• ✅ Case-insensitive matching: GET, get, and Get all work
• ✅ Backward compatibility: Existing export default handlers continue to work
• ✅ Smart fallback: Method-specific exports take precedence, falls back to default export
• ✅ Proper 405 handling: Returns 405 Method Not Allowed with correct Allow header when no handlers exist
• ✅ Preserved behavior: Maintains existing req.params assignment and hook emission

Usage Examples

New method-specific pattern:

// api/users.js
export function GET(req, res) {
  res.json({ users: await getUsers() })
}

export function POST(req, res) {
  const user = await createUser(req.body)
  res.json({ user })
}

export function PUT(req, res) {
  const user = await updateUser(req.params.id, req.body)
  res.json({ user })
}

Legacy pattern (still supported):

// api/legacy.js
export default function handler(req, res) {
  if (req.method === 'GET') {
    res.json({ data: 'legacy handler' })
  } else {
    res.statusCode = 405
    res.end('Method Not Allowed')
  }
}

Mixed pattern:

// api/mixed.js
export function GET(req, res) {
  res.json({ data: 'specific GET handler' })
}

// Fallback for all other methods
export default function handler(req, res) {
  res.statusCode = 405
  res.end('Only GET is supported')
}

Testing

• Added comprehensive test suites covering all functionality
• 25 new tests ensuring correct dispatch logic, fallback behavior, and edge cases
• All existing tests continue to pass, confirming no regressions
• TypeScript compilation verified

Benefits

• Cleaner code: No more manual method checking in handlers
• Better DX: Method-specific exports are more intuitive and easier to maintain
• Type safety: Full TypeScript support for both patterns
• Zero breaking changes: Existing code continues to work unchanged
• Automatic 405 handling: No need to manually implement Method Not Allowed responses

Fixes requirements for method-specific API handler exports with proper fallback behavior and TypeScript support.

This pull request was created as a result of the following prompt from Copilot chat.

Implement method-specific exports for API handlers, allowing named exports like export const GET = (req, res) => {...} in addition to the legacy default export. Update the dispatch logic in adex/runtime/handler.js to:

1. Check for method-specific exports matching the HTTP method (case-insensitive).
2. Fall back to module.default if no method-specific export exists.
3. Return 405 Method Not Allowed if neither exists.
4. Support GET, POST, PUT, PATCH, DELETE, OPTIONS, HEAD.
5. Maintain req.params assignment and hook emission behavior.

Also:

• Update TypeScript types in adex/src/http.d.ts to support both patterns.
• Ensure the solution passes linting and compilation.
• Do not alter unrelated code.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.