如何在不使用setInterval / timeout的情况下检查实时更新？

Question

建立一个社交网络，我正在尝试获取实时通知。当前，站点使用setInterval每隔几秒钟发送一次AJAX请求。看起来像这样：

setInterval ( function(){
    url = base_dir+"/ajax/file.php";
    data = "data=someData";
    $.ajax({
        type: "POST",
        url: url,
        data: data,
        dataType: "json",
        beforeSend: function(x) {
            if(x && x.overrideMimeType) {
                x.overrideMimeType("application/json;charset=UTF-8");
            }
        },
        success: function(JSON){
            // retrieve data here   
        }
    });
}, 5000);

那很好，但是我非常担心创建服务器过载。我尝试了彗星技术，但由于某种原因，它发送的请求比上述代码多得多。还有其他更有用的技术来实时发布此数据吗？

编辑：为实现长轮询，我使用了以下内容（使用此处提到的示例：http :
//techoctave.com/c7/posts/60-simple-long-polling-example-with-javascript-and-
jquery
）：

(function poll(){
    url = base_dir+"/ajax/file.php";
    data = "data=someData";
    $.ajax({
        type: "POST",
        url: url,
        data: data,
        dataType: "json",
        beforeSend: function(x) {
            if(x && x.overrideMimeType) {
                x.overrideMimeType("application/json;charset=UTF-8");
            }
        },
        success: function(JSON){
            // retrieve data here   
        },
complete: poll,
timeout: 5000
    });
})();

我有可能无法正确理解彗星原理。

PHP代码：

// Checks for new notifications, and updates the title and notifications bar if there are any
 private static function NotificationsCounter (){
    //self::$it_user_id                                     = query that retrieves my id for further checks;                                                        
    //$friend_requests_count                                = query that retrieves the friend requests count;
    //$updates_count                                        = query that retrieves the updates count;               
    $total_notifications                                    = $friend_requests_count+$updates_count;

    if ($total_notifications > 0) $addToTitle = "(".$total_notifications.")";
    else $addToTitle = "";

    if ($updates_count > 0) $counterHTML = "<span class='notification_counter' id='updates_counter' style='float: right;'>".$updates_count."</span>";
    else $counterHTML = "";

    $data = array("counter"=>$total_notifications,"addToTitle"=>$addToTitle,"counterHTML"=>$counterHTML,);
    echo json_encode($data); // parse to json and print
}

由于Facebook也使用PHP，因此该怎么做？

Answer 1

您应该使用 websockets
。您可以连接到服务器并注册onmessage处理程序。只要服务器有任何要发送给客户端的内容，处理程序都会被调用。无需超时。

在浏览器中检查websocket支持。到目前为止，仅Chrome，Opera和Safari支持它们。

if ('WebSocket' in window){
   /* WebSocket is supported. You can proceed with your code*/
} else {
   /*WebSockets are not supported. Try a fallback method like long-polling etc*/
}

连接中

var connection = new WebSocket('ws://example.org:12345/myapp');

处理程序

connection.onopen = function(){
   console.log('Connection open!');
}

connection.onclose = function(){
   console.log('Connection closed');
}

connection.onmessage = function(e){
   var server_message = e.data;
   console.log(server_message);
}

文档：http : //www.developerfusion.com/article/143158/an-introduction-to-
websockets/