index.html

<script>
if (!!window.EventSource) {
  var source = new EventSource('serverSentEvent.php');
} else {
  // Result to xhr polling :(
}
source.addEventListener('message', function(e) {
  console.log(e.data);
}, false);

source.addEventListener('open', function(e) {
  // Connection was opened.
}, false);

source.addEventListener('error', function(e) {
  if (e.readyState == EventSource.CLOSED) {
    // Connection was closed.
  }
}, false);
</script>