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doc: clarify fd behaviour with {read,write}File #23706

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doc: clarify fd behaviour with {read,write}File #23706

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351d9df
doc: clarify fd behaviour with {read,write}File
thefourtheye Oct 17, 2018
5370c14
address @vsemozhetbyt's comments
thefourtheye Oct 19, 2018
b5a440c
changes because of #23709
thefourtheye Oct 19, 2018
d44bf9f
group the relevant parts
thefourtheye Oct 19, 2018
121e1dd
update fs promisified functions' behaviour
thefourtheye Oct 19, 2018
9975e9a
Revert "changes because of #23709"
thefourtheye Oct 24, 2018
ef290a7
address review comments
thefourtheye Oct 24, 2018
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22 changes: 16 additions & 6 deletions doc/api/fs.md
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Original file line number Diff line number Diff line change
Expand Up @@ -2547,10 +2547,13 @@ fs.readFile('<directory>', (err, data) => {
});
```

Any specified file descriptor has to support reading.

If a file descriptor is specified as the `path`, it will not be closed
### File Descriptors
1. Any specified file descriptor has to support reading.
2. If a file descriptor is specified as the `path`, it will not be closed
automatically.
3. The reading will begin at the current position. If the file size is
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@ChALkeR ChALkeR Oct 24, 2018 •
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Clarify that the If ... is an example?
Something like E.g., if ... or For example, if ....

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Ack.

10 bytes and if six bytes are already read with this file descriptor, then
`readFile` will return only the rest of the four bytes.
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Nit:

Suggested change
`readFile` will return only the rest of the four bytes.
`readFile()` will return only the rest of the four bytes.


The `fs.readFile()` function buffers the entire file. To minimize memory costs,
when possible prefer streaming via `fs.createReadStream()`.
Expand Down Expand Up @@ -3540,14 +3543,21 @@ If `options` is a string, then it specifies the encoding:
fs.writeFile('message.txt', 'Hello Node.js', 'utf8', callback);
```

Any specified file descriptor has to support writing.
### File Descriptors
1. Any specified file descriptor has to support writing.
2. If a file descriptor is specified as the `file`, it will not be closed
automatically.
3. The writing will begin at the beginning of the file. If the file size
is 10 bytes and if six bytes are written with this file descriptor, then
`writeFile` will return six bytes newly written and four bytes from the file.
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This seems a bit confusing as writeFileSync() returns undefined and writeFile() transfers only error to the calback. Maybe something like this this?

Suggested change
`writeFile` will return six bytes newly written and four bytes from the file.
the file contents would be six bytes newly written and four bytes from the file.

For example, if the file already had `'Hello World'` and the newly written
content is `'Aloha'`, then the contents of the file would be `'Aloha World'`,
rather than just `'Aloha'`.

It is unsafe to use `fs.writeFile()` multiple times on the same file without
waiting for the callback. For this scenario, [`fs.createWriteStream()`][] is
recommended.

If a file descriptor is specified as the `file`, it will not be closed
automatically.

## fs.writeFileSync(file, data[, options])
<!-- YAML
Expand Down