Example error handler in node.js for APIs

error-handler.js

const express = require("express");

const app = express();

const PORT = process.env.PORT || 3001;

// Replace with your logger
const logger = console;

/**
 * Create the errors to send to the client
 */
class AppError extends Error {
  constructor(tag, message, status = 500, cause = null) {
    super(message);
    this.tag = tag;
    this.status = status;
    this.cause = cause;
  }
}

// Example endpoint to send random error
app.get("/hello", (req, res, next) => {
  if (Math.random() < 0.5) {
    return res.json({ msg: "world" });
  }
  return next(new AppError("hello_handler", "Can't resolve the current service is failed", 503));
});

// Middleware to handle all the errors in the app and log in your custom logger (datadog, newrelic)
app.use((error, req, res, next) => {
  if (error) {
    const { tag, status = 500, message } = error;

    logger.error(`[${tag}] ${status} - ${message}`);

    return res
      .status(status)
      .json({ message: message || "Internal Server Error" });
  }

  return next();
});

app.listen(PORT, () => {
  logger.info(`API listen in ${PORT}`);
});