emitter.js

// Testing EventEmitter and Promise, async/await

const EventEmitter = require('events');
const http = require('http');
const fs = require('fs').promises;

const myEmitter = new EventEmitter();

async function handler3() {
  console.log('handler3: myevent was fired! test Promise');

  console.log('reading emitter.js with then');
  fs.readFile('./emitter.js', { encoding: 'utf8' }).then(content => console.log(`then: read ${content.length} from emitter.js`));

  console.log('reading emitter.js with await');
  let content = await fs.readFile('./emitter.js', { encoding: 'utf8' });
  console.log(`await: read ${content.length} from emitter.js`);

  console.log('handler3 ended');
}

async function main() {
  myEmitter.on('myevent', () => console.log('handler1: myevent was fired!'));

  myEmitter.on('myevent', () => {
    console.log('handler2: myevent was fired! test callback function');

    http.get('http://nodejs.org/dist/index.json', (res) => {
      const { statusCode } = res;
      const contentType = res.headers['content-type'];

      let error;
      if (statusCode !== 200) {
        error = new Error('Request Failed.\n' +
                          `Status Code: ${statusCode}`);
      } else if (!/^application\/json/.test(contentType)) {
        error = new Error('Invalid content-type.\n' +
                          `Expected application/json but received ${contentType}`);
      }
      if (error) {
        console.error(error.message);
        // Consume response data to free up memory
        res.resume();
        return;
      }

      res.setEncoding('utf8');
      let rawData = '';
      res.on('data', (chunk) => { rawData += chunk; });
      res.on('end', () => {
        console.log('GET callback completed');
        try {
          const parsedData = JSON.parse(rawData);
          console.log(parsedData[0].version);
        } catch (e) {
          console.error(e.message);
        }
      });
    }).on('error', (e) => {
      console.error(`Got error: ${e.message}`);
    });
  });

  // 1. await is not waited, comment out 2. to easily see test result
  myEmitter.on('myevent', handler3);

  console.log('emitting event');
  myEmitter.emit('myevent');
  console.log('emitted event');

  // 2. await is waited, comment out 1. to easily see test result
  /*console.log('before handler3');
  await handler3();
  console.log('after handler3');*/

  console.log('>>> I am the last log line');
}

(async function () {
  await main();
})();