What is the difference between res.send and res.write in express?
res.send
res.sendis only in Express.js.- Performs many useful tasks for simple non-streaming responses.
- Ability to automatically assigns the
Content-LengthHTTP response header field. - Ability to provides automatic HEAD & HTTP cache freshness support.
- Practical explanation
res.sendcan only be called once, since it is equivalent tores.write+res.end()- Example:
app.get('/user/:id', function (req, res) { res.send('OK');});
For more details:
res.write
- Can be called multiple times to provide successive parts of the body.
- Example:
response.write('<html>');response.write('<body>');response.write('<h1>Hello, World!</h1>');response.write('</body>');response.write('</html>');response.end();
For more details:
res.send is equivalent to res.write + res.endSo the key difference is res.send can be called only once where as res.write can be called multiple times followed by a res.end.
But apart from that res.send is part of Express. It can automatically detect the length of response header.But there may be be a chance of memory spike with res.send(), in case of large files, our application hangs in between .
One of the most important differences not indicated in any of the answers are "draining".
The res.write may return true or false. As of the documentation:
Returns true if the entire data was flushed successfully to the kernel buffer. Returns false if all or part of the data was queued in user memory. 'drain' will be emitted when the buffer is free again.
So, when doing res.write, the caller should hold off writing until the drain event emits if the res.write returned false.
All these are handled automatically in res.send. The trade off is the buffering you will have to do when using the latter.