I have created a node module following this recipe:

mkdir addon
cd addon
npm init -y
npm install --save-dev node-gyp
npm install node-addon-api

Create the file addon.cc:

#include <napi.h>

Napi::String Hello(const Napi::CallbackInfo& info) {
  Napi::Env env = info.Env();
  return Napi::String::New(env, "Hello from C++!");
}

Napi::Object Init(Napi::Env env, Napi::Object exports) {
  exports.Set(Napi::String::New(env, "hello"),
              Napi::Function::New(env, Hello));
  return exports;
}

NODE_API_MODULE(addon, Init)

create the file binding.gyp

{
  "targets": [
    {
      "target_name": "addon",
      "sources": [ "addon.cc" ],
      'include_dirs': [
            "<!@(node -p "require('node-addon-api').include")"
        ],
        'libraries': [],
        'dependencies': [
            "<!(node -p "require('node-addon-api').gyp")"
        ],
        'defines': [ 'NAPI_DISABLE_CPP_EXCEPTIONS' ]
    }
  ]
}

npm configure
npm build

copy the file addon/build/Release/addon.node > lib/addon/addon.node

Create a file in app/api/test/route.ts

import { NextResponse } from "next/server";

const myAddon = require("/lib/addon/addon.node")

export async function GET() {

  try {
    const result = myAddon.hello();
    return NextResponse.json({
      message: result
    });
  } catch(error) {
    return NextResponse.json({
      message: error.message
    });
  }
  
}

in app/page.tsx I have:

"use client";
import { useEffect, useState } from "react";

export default function Home() {
  const [message, setMessage] = useState<string>("default");

  const getData = async () =>
    fetch("/api/hello")
      .then(function (response) {
        return response.text();
      })
      .then(function (data_raw) {
        const data = JSON.parse(data_raw);
        setMessage(data.message);
      });

  useEffect(() => {
    getData();
  }, []);

  return (
    <main className="p-24">
      {message}
    </main>
  );
}

I get the error when running npm run dev:

[NEXT] Import trace for requested module:
[NEXT] ./lib/addon/addon.node
[NEXT] ./src/app/api/hello/route.ts
[NEXT]  ⨯ ./lib/addon/addon.node
[NEXT] Module parse failed: Unexpected character '�' (1:2)
[NEXT] You may need an appropriate loader to handle this file type, currently no loaders are configured to process this file. See https://webpack.js.org/concepts#loaders
[NEXT] (Source code omitted for this binary file)

Why do I get this “unexpected character”? How can I fix it?