fs: is fs.unwatchFile() available on Windows?

Version: v4 – master
Platform: Windows 7 x64
Subsystem: fs

Create a script:

'use strict';

const fs = require('fs');

fs.watchFile(__filename, { interval: 1000 }, (current, previous) => {
  console.log(current.size, previous.size);
  fs.unwatchFile(__filename, () => { console.log('File unwatched'); });
  console.log('unwatchFile() called');
});

Launch it, then change and save several times.
Expected output:

275 274
unwatchFile() called
File unwatched
[exit]

Real output

275 274
unwatchFile() called
276 275
unwatchFile() called
277 276
unwatchFile() called
[.., no exit]

I cannot find any caveats in fs doc about this. Is there any?

This works as intended:

'use strict';

const fs = require('fs');

const watcher = fs.watch(__filename, (eventType) => {
  console.log(eventType);
  watcher.close();
  console.log('watcher.close() called');
});

change
watcher.close() called
[exit]

The listener argument passed to fs.unwatchFile should be a callback function that was previously registered with fs.watchFile and is not expected to be called as part of the invocation of fs.unwatchFile.

To clarify, in your example the fs.unwatchFile call does not remove the listener registered with the fs.watchFile call so never exits because there is still an active registered callback.

@richardlau

@richardlau Thank you! This do work as intended:

'use strict';

const fs = require('fs');

const listener = (current, previous) => {
  console.log(current.size, previous.size);
  fs.unwatchFile(__filename, listener);
  console.log('unwatchFile() called');
}

fs.watchFile(__filename, { interval: 1000 }, listener);

I was misguided by the listener signature in last descriptions:

https://nodejs.org/download/nightly/v10.0.0-nightly20180122e7ff00d0c5/docs/api/fs.html#fs_fs_unwatchfile_filename_listener

Is this signature intended? Added here: #13424

doc: remove confusing signature in fs.md

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fs: is fs.unwatchFile() available on Windows? #18305

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fs: is fs.unwatchFile() available on Windows? #18305

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vsemozhetbyt commented on Jan 23, 2018

richardlau commented on Jan 23, 2018

richardlau commented on Jan 23, 2018

vsemozhetbyt commented on Jan 23, 2018

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