errorMiddleware not working as expected in express - node.js

Question

My errorHandler middleware is not showing up the response.
Instead of giving the error in json format as I have coded, it still shows the error in html format. Where did i go wrong?
app.js
import express from "express";
import dotenv from "dotenv";
import connectDB from "./config/db.js";
import colors from "colors";
import productRoutes from "./routes/productRoutes.js";
import errorHandler from "./middlewares/errorMiddleware.js";
dotenv.config();
// Connecting to MongoDB
connectDB();
// Express specific
const app = express();
// Middlewares
app.use(errorHandler);
app.use("/api/products", productRoutes);
app.use("/api/products/:id", productRoutes);
const PORT = process.env.PORT || 5000;
app.listen(
PORT,
console.log(
`Server running in ${process.env.NODE_ENV} mode on port ${PORT}`.yellow.bold
)
);
errorMiddleware.js
const errorHandler = (err, req, res, next) => {
const statusCode = res.statusCode === 200 ? 500 : res.statusCode; //we sometimes get 200 code (ok) even if its error. 500 means server error
res.status(statusCode);
res.json({
message: err.message,
stack: process.env.NODE_ENV === "production" ? null : err.stack,
});
};
export default errorHandler;
Output:
expected Output:
{
message: ...
stack: ...
}

Answer 1

You define error-handling middleware last, after other app.use() and routes call
source
Here is the basic working example
import express from "express";
const app = express();
app.use('/api/products', (req, res) => {
throw new Error('Triggers an error');
});
// Do other routes here and keep error handling below.
app.use((err, req, res, next) => {
res.status(res.statusCode);
res.json({
message: err.message,
stack: process.env.NODE_ENV === "production" ? null : err.stack,
});
})
const PORT = process.env.PORT || 5000;
app.listen(PORT, () => {
console.log(`Server started on port ${PORT}`);
});
Your only mistake is defining the middleware order.