HTML5 服务器发送事件（server-sent event）允许网页获得来自服务器的更新

JS端 实例化EventSource对象，并且实现监听

$("#getFile").click(function () {
       //监听IP+URLP 推送的消息
        var source = new EventSource(IP + URLP);
 
        source.onmessage = function (event) {
            alert(event.data);
          //如果不close(),每隔3-5s会再次收到推送
            source.close();
        };
 
    });  

 

服务端 

context.Response.ContentType = "text/event-stream";
context.Response.CacheControl = "no-cache"
context.Response.Write("data:" + fileId + "\n\n"); 
// \n\n 就相当于 context.Response.Flush();