What is the difference between res.send and res.write in express?

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I am a beginner to express.js and I am trying to understand the difference between res.send and res.write ?

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余生分开走

2020-12-04 19:39
Suppose you have two line that needs to be shown up and you use res.send as
```
res.send("shows only First Line")
res.send("won't show second Line")
```
Then only first line will show up, whereas using res.write you have flexibility to write multiple line such as
```
res.write("Shows first line")
res.write("Shows second line")
res.send()
```
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轻奢々

2020-12-04 19:44
res.send
- res.send is only in Express.js.
- Performs many useful tasks for simple non-streaming responses.
- Ability to automatically assigns the Content-Length HTTP response header field.
- Ability to provides automatic HEAD & HTTP cache freshness support.
- Practical explanation
  - res.send can only be called once, since it is equivalent to res.write + res.end()
  - Example:
```
app.get('/user/:id', function (req, res) {
    res.send('OK');
});
```
For more details:
- Express.js: Response
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:
- response.write(chunk[, encoding][, callback])
- Anatomy of an HTTP Transaction: Sending Response Body
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误落风尘

2020-12-04 19:47

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.

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天命终不由人

2020-12-04 20:01

res.send is equivalent to res.write + res.end So 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 .

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