Node.js API compatibility - Events

/**
 * An example of using the Node.js `events` module in Azion Functions.
 * Support:
 * - Partial support
 * - Extended by library `events`
 * @example
 * // Execute with Azion Bundler:
 * npx edge-functions build
 * npx edge-functions dev
 */
import { EventEmitter } from "node:events";

/**
 * Emit an event and listen to it.
 * @param {*} event
 * @returns {Response} Response
 */
const main = async (event) => {
  const emitter = new EventEmitter();

  emitter.on("hello-event", (...args) => {
    console.log("an event occurred!", ...args);
  });

  emitter.emit("hello-event", 1, 2, 3);
  return new Response("Event emitted", { status: 200 });
};

export default main;

import { EventEmitter } from "node:events";

const main = async (event) => {
  const requestEmitter = new EventEmitter();
  const results = [];

  // Get request info with optional chaining for safety
  const requestUrl = event.request?.url || "https://default.example.com";
  const requestHeaders = event.request?.headers || {};

  // Listen for request start
  requestEmitter.on("start", (url) => {
    console.log(`Processing request: ${url}`);
    results.push(`Started: ${url}`);
  });

  // Listen for validation events
  requestEmitter.on("validate", (data) => {
    if (data.headers) {
      console.log("Headers validated");
      results.push("Headers validated");
    }
  });

  // Listen for completion
  requestEmitter.on("complete", (status) => {
    console.log(`Request completed with status: ${status}`);
    results.push(`Completed: ${status}`);
  });

  // Listen for errors
  requestEmitter.on("error", (err) => {
    console.error(`Error: ${err.message}`);
    results.push(`Error: ${err.message}`);
  });

  // Emit events in sequence
  requestEmitter.emit("start", requestUrl);
  requestEmitter.emit("validate", { headers: requestHeaders });
  requestEmitter.emit("complete", 200);

  return new Response(JSON.stringify({ events: results }), {
    headers: { "Content-Type": "application/json" }
  });
};

export default main;

import { EventEmitter } from "node:events";

const main = async (event) => {
  const emitter = new EventEmitter();
  const log = [];

  // One-time listener - only executes once
  emitter.once("init", () => {
    console.log("Initialization complete");
    log.push("Initialized");
  });

  // Multiple listeners for same event
  emitter.on("data", (chunk) => {
    console.log(`Processing chunk: ${chunk}`);
    log.push(`Chunk: ${chunk}`);
  });

  emitter.on("data", (chunk) => {
    console.log(`Logging chunk: ${chunk}`);
    log.push(`Logged: ${chunk}`);
  });

  // Error handling - special 'error' event
  emitter.on("error", (err) => {
    console.error(`Error caught: ${err.message}`);
    log.push(`Error: ${err.message}`);
  });

  // Emit events
  emitter.emit("init");
  emitter.emit("init"); // Won't trigger again - once() used
  emitter.emit("data", "chunk-1");
  emitter.emit("data", "chunk-2");
  emitter.emit("error", new Error("Test error"));

  return new Response(JSON.stringify({ log }), {
    headers: { "Content-Type": "application/json" }
  });
};

export default main;

import { EventEmitter } from "node:events";
import { setTimeout } from "node:timers/promises";

const main = async (event) => {
  const emitter = new EventEmitter();
  const results = [];

  // Note: EventEmitter does NOT await Promises returned by listeners.
  // The emit() method returns immediately, without waiting for async operations.
  // For async operations, it's recommended to use Promise-based patterns
  // instead of relying on EventEmitter alone.

  // Listen for fetch completion events
  emitter.on("fetched", (result) => {
    results.push(result);
    console.log(`Fetched: ${result.url}`);
  });

  // Error handler
  emitter.on("error", (err) => {
    console.error(`Fetch error: ${err.message}`);
    results.push({ error: err.message });
  });

  // Define async fetch function that emits events
  const fetchData = async (url) => {
    try {
      const response = await fetch(url);
      const data = await response.json();
      const result = { url, status: response.status, data };
      emitter.emit("fetched", result);
      return result;
    } catch (error) {
      emitter.emit("error", error);
      return { url, error: error.message };
    }
  };

  // URLs to fetch
  const urls = [
    "https://jsonplaceholder.typicode.com/todos/1",
    "https://jsonplaceholder.typicode.com/todos/2"
  ];

  // Execute fetches in parallel and wait for completion
  const fetchResults = await Promise.all(urls.map(fetchData));

  return new Response(JSON.stringify({
    results,
    fetchResults
  }), {
    headers: { "Content-Type": "application/json" }
  });
};

export default main;

import { EventEmitter } from "node:events";

// Custom class extending EventEmitter
class RequestHandler extends EventEmitter {
  constructor() {
    super();
    this.requestCount = 0;
  }

  processRequest(request) {
    this.requestCount++;
    this.emit("request", { id: this.requestCount, url: request.url });

    try {
      // Simulate processing
      const result = { processed: true, id: this.requestCount };
      this.emit("success", result);
      return result;
    } catch (error) {
      this.emit("error", error);
      throw error;
    }
  }
}

const main = async (event) => {
  const handler = new RequestHandler();
  const logs = [];

  // Attach listeners
  handler.on("request", (data) => {
    logs.push(`Request #${data.id}: ${data.url}`);
  });

  handler.on("success", (result) => {
    logs.push(`Success: ${JSON.stringify(result)}`);
  });

  handler.on("error", (err) => {
    logs.push(`Error: ${err.message}`);
  });

  // Process requests
  handler.processRequest(event.request);
  handler.processRequest({ url: "https://example.com/test" });

  // Get listener counts
  const listenerCount = handler.listenerCount("request");
  logs.push(`Request listeners: ${listenerCount}`);

  return new Response(JSON.stringify({ logs, totalRequests: handler.requestCount }), {
    headers: { "Content-Type": "application/json" }
  });
};

export default main;