event-source-4.html

<script src="event-source-4.js"></script>

event-source-4.js

document.addEventListener('DOMContentLoaded', function () {
  
  
  //  TESTING PARAMS TO EVENT SOURCE
  var params    = 'foo=bar',
      eventSrc  = new EventSource('event-source-4.php?' + params);
  
  console.time('EventSource Opened');
  console.group('EventSource Created');
  console.dir( eventSrc );
  console.groupEnd();
  
  
  eventSrc.addEventListener('open', function (event) {
    console.timeEnd('EventSource Opened');
    
    console.time('Time Elapsed between open and message');
    console.log('Event Fired (Open)');
  });
  
  eventSrc.addEventListener('message', function (event) {
    
    console.timeEnd('Time Elapsed between open and message');

    console.group('MessageEvent Fired');
    console.log(event);

    var data  = JSON.parse(event.data);

    console.group('event.data');
    for ( var prop in data ) {
      console.log(prop + '=' + data[prop]);
    }
    console.groupEnd('event.data');
    
    console.groupEnd('MessageEvent Fired');    
  });
}, false);

event-source-4.php

<?php
header("Content-Type: text/event-stream\n\n");

echo 'data: ' . json_encode($_GET) . "\n";
?>