Express middleware before response is carried out to client

Question

I need to modify the response data a module sends to the client, as the module uses res.send i can't seem to figure out a way for me to modify the data before it's carried out to the client.

Is there any kind of middleware/event that I can use to catch the res.send and modify the data before its executed?

I am aware that router.use exists but it's called before the router.post function and not before the res.send is sent to the client. So I need some kind of middleware which is called after the router.post function is done but before anything is sent to the client.

Answer 1

Well you can override the send function:

app.use(function (req, res) {
    var send = res.send;
    res.send = function (body) { // It might be a little tricky here, because send supports a variety of arguments, and you have to make sure you support all of them!
        // Do something with the body...
        send.call(this, body);
    };
});

If you want to support more than just calling send(like calling end method), then you have to override more functions...

You can check connect-livereload on how it adds a script to any html output.

Answer 2

One more solution from here:

expressApp.use(function (req, res, next) {
    req.on("end", function () {
        console.log('on request end');
    });
    next();
});