api-utils.ts

import { NextApiRequest, NextApiResponse } from "next";

export async function handleApiRequest(
  req: NextApiRequest,
  res: NextApiResponse,
  expectedReqMethod: string,
  handleRequest: (body: any) => Promise<any>
): Promise<void> {
  if (req.method === expectedReqMethod) {
    try {
      const responseData = await handleRequest(req.body);
      res.status(200).json(responseData);
    } catch (error: unknown) {
      handleErrorResponse(res, error);
    }
  } else {
    res.status(405).json({ error: "Method not allowed" });
  }
}

export function handleErrorResponse(
  res: NextApiResponse,
  error: unknown
): void {
  if (error instanceof Error) {
    res.status(500).json({ error: error.message });
  } else {
    res.status(500).json({ error: "An unknown error occurred" });
  }
}

Example usage for handling both GET and POST requests:

// pages/api/messages.ts
import { NextApiRequest, NextApiResponse } from "next";
import { handleApiRequest } from "@/utils/api-utils";

const messages: string[] = [];

async function handleGetMessages() {
  return { messages };
}

async function handleCreateMessage(body: any) {
  const { message } = body;

  if (!message || typeof message !== "string") {
    throw new Error("Invalid message");
  }

  messages.push(message);
  return { success: true };
}

export default async function handler(
  req: NextApiRequest,
  res: NextApiResponse
) {
  if (req.method === "GET") {
    await handleApiRequest(req, res, "GET", handleGetMessages);
  } else if (req.method === "POST") {
    await handleApiRequest(req, res, "POST", handleCreateMessage);
  } else {
    res.status(405).json({ error: "Method not allowed" });
  }
}