我正在设置一个系统，其中我使用JS Server-Sent_Events与PHP。而且效果很好。但是在每一次运行中，错误事件都会被触发一次，我不明白为什么。
我的JS：

var source = new EventSource("serverSideEvents.php");
source.onmessage = function(event) {
     var data =  $.parseJSON(event.data);
     $(data).each(function(){
            doSomethingWith(this); //works as expected
      });
};
source.onerror = function(event) {
   console.log(event); //fires every few seconds don't know why
};

我的php：

<?php
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache'); 
  sendUpdates( );
function sendUpdates() {
  $controller = new someController();
  $out = $controller->Run();
  foreach($out as $msg)
    sendSSEMessage($msg['id'], 'data:'.json_encode($msg));
}
function sendSSEMessage( $id, $data ){
  echo "id: $id \n$data \n\n";
  ob_flush();
  flush();
}

这工作正常，在PHP或浏览器上，PHP不会抛出错误，但每次运行PHP时都会触发js SSE的错误事件。这是控制台中的错误：

Event {isTrusted: true, type: "error", target: EventSource, currentTarget: EventSource, eventPhase: 2, …}
bubbles:false
cancelBubble:false
cancelable:false
composed:false
currentTarget:
EventSource {url: "http://localhost:7790/serverSideEvents.php", withCredentials: false, readyState: 0, onopen: null, onmessage: ƒ, …}
defaultPrevented:false
eventPhase:0
isTrusted:true
path:[]
returnValue:true
srcElement:EventSource {url: "http://localhost:7790/serverSideEvents.php", withCredentials: false, readyState: 0, onopen: null, onmessage: ƒ, …}
target:EventSource {url: "http://localhost:7790/serverSideEvents.php", withCredentials: false, readyState: 0, onopen: null, onmessage: ƒ, …}
timeStamp:1129162.5250000001
type:"error"
__proto__:Event

要澄清的是：代码按预期工作。我得到了我需要的服务器消息。而且触发错误事件。