Async Handler Type Declaration

TODO: collapasable, copyable, download, etc

In TypeScript, how can I say a export const withMetrics = (handler: (req: Request | NextApiRequest, res: NextApiResponse) => void) => { accepts an async handler function?To indicate that the handler function is async, you can update the type definition to specify that the function returns a Promise<void>. Here's how you can modify your code:

import { NextApiRequest, NextApiResponse } from 'next';

// Define the handler type as an async function
type AsyncHandler = (req: Request | NextApiRequest, res: NextApiResponse) => Promise<void>;

// Define the withMetrics function that accepts an async handler
export const withMetrics = (handler: AsyncHandler) => {
  return async (req: Request | NextApiRequest, res: NextApiResponse) => {
    // Your metric collection logic here
    
    try {
      // Call the async handler
      await handler(req, res);
    } catch (error) {
      // Handle any errors
      console.error('Error in handler:', error);
      res.status(500).send('Internal Server Error');
    }
    
    // Your additional logic here
  };
};

In this example:

1. AsyncHandler is defined as a type alias for an asynchronous function that takes req and res as parameters and returns a Promise<void>.

2. withMetrics is a higher-order function that takes an AsyncHandler and returns another async function. This returned function can then handle the request and response, incorporating any additional logic you need (like metric collection) before and after calling the handler.And when I go to use it... this isn't quite right, what would I do ? export const POST = withMetrics(async (req: Request | NextRequest, res: NextApiResponse) => {When using the withMetrics function with an async handler, you need to ensure that the types are compatible with the Next.js API handler. Here's the correct way to use it:

3. Define the POST function using withMetrics.

4. Ensure that the req parameter type is compatible with Request or NextRequest and the res parameter type is NextApiResponse.

Here's how you can define and use it:

import { NextApiRequest, NextApiResponse } from 'next';
import { withMetrics } from './path-to-withMetrics'; // adjust the import path as needed

// Define the async handler function
const handler = async (req: Request | NextApiRequest, res: NextApiResponse) => {
  // Your handler logic here
  res.status(200).json({ message: 'Success' });
};

// Wrap the handler with the withMetrics function
export const POST = withMetrics(handler);

In this example:

1. The handler function is defined as an async function that takes req and res parameters.
2. The handler is wrapped with the withMetrics function to create the POST function.
3. The withMetrics function ensures that the async handler is called and any necessary metric collection or additional logic is handled.

This should ensure that your POST function is correctly set up to work with Next.js API routes and can handle both Request and NextRequest types.

Async Handler Type Declaration created at Tue Jan 20 1970 20:36:53 GMT+0000 (Coordinated Universal Time)