What kind of error should be expected in a Next.js API route handler?

Question

What kind of error should be expected in a Next.js API route handler?

Recently, I encountered an issue with my API route handler:

import { NextRequest, NextResponse } from "next/server";
import dbConnect from "@/lib/dbConnect";
import User from "@/models/User";

interface ErrorMessage {
    message: string;
}

export async function GET(req: NextRequest, { params }: { params: { id: string } }) {
    await dbConnect();
    const { id } = params;

    try {
        const user = await User.findById(id)

        return NextResponse.json({
            success: true,
            data: user,
        }, {
            status: 200,
        })
    } catch (error: ErrorMessage) {
        return NextResponse.json({
            success: false,
            message: error.message
        }, {
            status: 404,
        })
    }
}

Upon encountering the TypeScript error

Catch clause variable type annotation must be 'any' or 'unknown' if specified.ts(1196)

, I realized that I still have a lot to learn about TypeScript best practices. Here's the screenshot of the error:

https://i.stack.imgur.com/Nsvqr.png

This occurred while working with Next.js version 13.4.16 and as a newcomer to TypeScript, I'm eager to improve my skills in dealing with such errors.

javascript typescript next.js

Answer 1

Answer №1

To handle any type of exception that may be thrown, it's important to type it as "any" or "unknown" (or simply omit the type).

One approach is to create "user-defined type guard" functions for checking types. You can refer to https://www.typescriptlang.org/docs/handbook/2/narrowing.html#using-type-predicates

For example:

function isErrorMessage(error: any): error is ErrorMessage {
  return typeof error?.message === "string";
}

try {
  //[...]
} catch (error) {
  if(isErrorMessage(error)){
    return NextResponse.json({
        success: false,
        message: error.message
      },
      { status: 404 }
    );
  }else{
    //example what we could do, if we do not know the error
    console.error(error)
    return NextResponse.json({
        success: false,
        message: 'internal server error'
      },
      { status: 500 }
    );
  }
}

Answer 2

To handle any type of exception that may be thrown, it's important to type it as "any" or "unknown" (or simply omit the type).

One approach is to create "user-defined type guard" functions for checking types. You can refer to https://www.typescriptlang.org/docs/handbook/2/narrowing.html#using-type-predicates

For example:

function isErrorMessage(error: any): error is ErrorMessage {
  return typeof error?.message === "string";
}

try {
  //[...]
} catch (error) {
  if(isErrorMessage(error)){
    return NextResponse.json({
        success: false,
        message: error.message
      },
      { status: 404 }
    );
  }else{
    //example what we could do, if we do not know the error
    console.error(error)
    return NextResponse.json({
        success: false,
        message: 'internal server error'
      },
      { status: 500 }
    );
  }
}

What kind of error should be expected in a Next.js API route handler?

Answer №1

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