Posted on Dec 31, 2023 • Edited on Jan 26, 2024

How to: Next.js API Global Errors & Auth Middleware

#nextjs #typescript #errors #authentication

This one's going to be quick. no bs. I was working on a Next.js project and needed a way to handle API Route Errors Globally. Similar to Express in Node.js.
This is what I've come up with and it works wonders for my setup.

We create a handler function that will take multiple handlers and run them one by one.

import { ApiError } from "next/dist/server/api-utils"; import { NextResponse, NextRequest } from "next/server"; export const custom_middleware = (...handlers: Function[]) => async (req: NextRequest, res: NextResponse) => { try { for (const handler of handlers) { await handler(req, res); } } catch (error) { if (error instanceof ApiError) { return NextResponse.json( { message: error.message }, { status: error.statusCode } ); } else { /// Log server errors using winston or your preferred logger console.log(error); return NextResponse.json( { message: "Server died for some reason" }, { status: 500 } ); } } };

Now we can add it to a route

/// app/api/ping/route.ts import { custom_middleware } from "@/app/lib/server/middleware"; import { ApiError } from "next/dist/server/api-utils"; import { NextRequest, NextResponse } from "next/server"; const main_handler = (req: NextRequest, res: NextResponse) => { const isAuthenticated = false; if (isAuthenticated) { return NextResponse.json({ success: true }); } throw new ApiError(400, "Some error"); }; export const GET = custom_middleware(main_handler);

We can see the fruits of our labour in the browser itself.
We can add our own custom authentication logic here too.

export const auth_middleware = async (req: NextRequest, res: NextResponse) => { /// Your auth logic const isAuthenticated = false; if (!isAuthenticated) { throw new ApiError(401, "Unauthorized"); } };

Call it in our middleware_handler

export const custom_middleware = (...handlers: Function[]) => async (req: NextRequest, res: NextResponse) => { try { /// /// Auth middleware await auth_middleware(req, res); for (const handler of handlers) { await handler(req, res); } } catch (error) { if (error instanceof ApiError) { return NextResponse.json( { message: error.message }, { status: error.statusCode } ); } else { /// Log server errors using winston or your preferred logger console.log(error); return NextResponse.json( { message: "Server died for some reason" }, { status: 500 } ); } } };