服务器在 AJAX 请求后发送多个响应 - 使用 Socket.IO 和 ExpressJS

Question

I'm trying to build a real-time program where users can set a marker on a Google Map and others who are connected can get that same marker. Everything seems to work fine except that after a few minutes, the server side is submitting the data a second time.

To clarify: client sets a marker on the map, the marker is sent to the server, running Node JS with Express JS, in JSON format. The server returns the data to all connected clients. Minutes later, the server sends the same data it received once more, causing a "ERR_EMPTY_RESPONSE" client-side on the last line of example "Client code".

Client code:

var data = new Array();

data.push({lat: Gmap.markers[0].lat, lng: Gmap.markers[0].lng});

var xhttp = new XMLHttpRequest();
xhttp.open("POST", "/marker", true);
xhttp.setRequestHeader('Content-type', 'application/json; charset=UTF-8');
xhttp.send(JSON.stringify(data));

Server-side:

var app = express():
app.post('/marker', function(req,res){
    io.emit('marker', req.body);
})

Anyone have any idea of whats going on?

Answer 1

You need to send a response to the http request. If you don't, the browser will time it out and may attempt to retry.

var app = express():
app.post('/marker', function(req,res){
    io.emit('marker', req.body);
    res.send("ok");     // <== Send a response to the http request here
})