old_contents: 'use strict';
  let WebSocketServer = require('ws').Server,
    wss = new WebSocketServer({ 'port': 1234 }),
    EddystoneBeacon = require('eddystone-beacon');
  
  wss.on('connection', ws => {
    ws.on('message', (url) => {
      console.log('received: ' + url);
      ws.send('received: ' + url);
  
      try {
        EddystoneBeacon.advertiseUrl(url);
        console.log('advertising: ' + url);
        ws.send('advertising: ' + url);
        console.log();
      } catch (e) {
        console.log('error: ' + e);
        ws.send('error: ' + e);
        console.log();
      }
    });
  });
  
new_contents: 'use strict';
  let WebSocketServer = require('ws').Server,
    wss = new WebSocketServer({ 'port': 1234 }),
    EddystoneBeacon = require('eddystone-beacon');
  
  wss.on('connection', ws => {
    ws.on('message', url => {
      console.log('received: ' + url);
      ws.send('received: ' + url);
  
      try {
        EddystoneBeacon.advertiseUrl(url);
        console.log('advertising: ' + url);
        ws.send('advertising: ' + url);
        console.log();
      } catch (e) {
        console.log('error: ' + e);
        ws.send('error: ' + e);
        console.log();
      }
    });
  });
  
subject: remove parenthesis for single argument arrow function