Difference between response.send and response.write in node js

Asked 13/2, 2014 at 9:11 Answered 17/12, 2016 at 19:5

I have written a small API which uses the Node js "restify" framework. This API receives a request (actually anything after "/") and then send that request to another server. Get the response back from server and passes the response back to original source of request. For this API I am using both restify server and client.

Below is that API code for better understanding.

var apiServer = require('apiServer');
apiServer.start();

var restify = require('restify');
var assert = require('assert');

function onRequest(request, response, next)
{
    var client = restify.createStringClient({ 
        url: 'http://example.com'
    });

    client.get('/' + request.params[0], function(err, req, res, data) {
        assert.ifError(err);

        response.setHeader('Content-Type', 'text/html');
        response.writeHead(res.statusCode);
        response.write(data);
        response.end();
    });
    next();
}

function start()
{
    var server = restify.createServer();
    server.get(/^\/(.*)/, onRequest);
    server.listen(8888);

    console.log("Server has started.");
}

exports.start = start;

Now I need to know the difference between response.write and response.send of Node.js. Because with response.write I can set header and write in it but it is not possible to do anything with headers when I use response.send. When I use response.send with setHeader() or writeHeader() I get this error:

http.js:691
    throw new Error('Can\'t set headers after they are sent.');
          ^
    Error: Can't set headers after they are sent.

There is also another thing. With response.send() I get the complete HTML output on the screen like:

<!DOCTYPE html>\n<html>\n\t<head></head></html> ..... "bla bla bla"

But with response.write I do not get the html on screen but only the text "bla bla bla".

It would be great if someone can explain me the differences.

Response answered 13/2, 2014 at 9:11 Comment(0)

I can't find response.send() in the docs, but I assume .send() will fill in and send the response so can only be called once, whereas .write() will just write the response, but you have to send it using response.end()

This means you can edit the headers using .write() because the response has not been sent yet.

EDIT :

response.send() is part of the restify Response API wrapper

Hebrides answered 13/2, 2014 at 9:17 Comment(3)

But what about the types of out that I received with those two functions? Like I said, res.write does not print the entire html on screen or browser but res.send does. – Response 13/2, 2014 at 9:38

@Response and also could you explain the differences in output a bit more? – Hebrides 13/2, 2014 at 9:52

res.send() is a deprecated method. see #30550549 – Stokes 22/2, 2017 at 10:40

response.send(msg) is equal to response.write(msg);response.end();

Which means, send can only be called once, write can be called many times, but you must call end yourself.

Vengeful answered 13/2, 2014 at 9:17 Comment(6)

But what about the types of out that I received with those two functions? Like I said, res.write does not print the entire html on screen or browser but res.send does. – Response 13/2, 2014 at 9:37

You want to display html code in browser? If so, just add head content-type, like response.writeHead('content-type','text/plain') – Vengeful 14/2, 2014 at 4:32

Basically, response.send(msg) is the same as response.end(msg). You just have to type an extra s. – Quadriga 2/2, 2015 at 19:17

@Quadriga This is not entirely true. Consider response.write("Hello");response.end(" World") vs response.write("Hello");response.send(" World"). The later would give me an error saying "Error: Can't set headers after they are sent." Not sure what is going on. – Amative 29/6, 2017 at 2:58

@Amative Look at the structure of an HTTP request -- by the time you've started sending the body of the request ("Hello") you have to have sent the headers already. send attempts to guess and set headers based on the type of the object you pass it, so it fails if the headers are already locked. – Allonge 30/5, 2018 at 22:17

@NicHartley Ah, I see – Amative 12/6, 2018 at 17:55

This means you can edit the headers using .write() because the response has not been sent yet.

EDIT :

response.send() is part of the restify Response API wrapper

Hebrides answered 13/2, 2014 at 9:17 Comment(3)

But what about the types of out that I received with those two functions? Like I said, res.write does not print the entire html on screen or browser but res.send does. – Response 13/2, 2014 at 9:38

@Response and also could you explain the differences in output a bit more? – Hebrides 13/2, 2014 at 9:52

res.send() is a deprecated method. see #30550549 – Stokes 22/2, 2017 at 10:40

res.send() is part of Express.js instead of pure Node.js.

Just an side observation. My app sometimes send back a very large Json object ( HighChart object that contains over 100k points). With res.send() sometimes it hangs and choke up the server, whereas res.write() and res.end() handle it just fine.

I also noticed a memory spike when res.send() is invoked.

Mortensen answered 30/9, 2014 at 18:40 Comment(3)

This is key! res.send is only in Express note Node. It also performs a bunch of magic like setting content-length and content-type. If you want to have absolute control, you need res.write and res.end. In fact the express compress module at this point only runs with res.write & res.end. – Horning 26/4, 2015 at 6:9

Woops disregard the whole not working in Express: github.com/expressjs/compression/issues/39 – Horning 26/4, 2015 at 6:21

working opposite at my end, res.send(json) is helping me to return a large json very fine whereas res.write(json) with res.end() doesn't do the job – Corniculate 24/5, 2017 at 6:27

I was trying to send huge text data(295mb) over http using res.send(data) and res.write(data). I noticed that res.send(data) is slower than res.write(data). I observed following things.

res.send(data): it can be called only once and it sends data in chunk of some buffer size to client and then again comes back and sends another chunk of buffer size so there is a lot of back and forth http communication.

res.write(data): It can be called multiple times followed by res.end() and It creates buffer size based on whole data and sends over http so it would be faster in case of huge amount of data.

Sharynshashlik answered 17/12, 2016 at 19:5 Comment(0)

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