node-watch

node-watch

A wrapper and enhancements for fs.watch.

Installation

npm install node-watch

Example

var watch = require('node-watch');

watch('file_or_dir', { recursive: true }, function(evt, name) {
  console.log('%s changed.', name);
});

Now it's fast to watch deep directories on macOS and Windows, since the recursive option is natively supported except on Linux.

// watch the whole disk
watch('/', { recursive: true }, console.log);

Why?

• Some editors will generate temporary files which will cause the callback function to be triggered multiple times.
• The callback function will only be triggered once on watching a single file.
• Missing an option to watch a directory recursively.
• Recursive watch is not supported on Linux or in older versions of nodejs.
• Keep it simple, stupid.

Options

The usage and options of node-watch are compatible with fs.watch.

• persistent: Boolean (default true)
• recursive: Boolean (default false)
• encoding: String (default 'utf8')

Extra options

• filter: RegExp | Function

  Return that matches the filter expression.

  // filter with regular expression
  watch('./', { filter: /\.json$/ });
  
  // filter with custom function
  watch('./', { filter: f => !/node_modules/.test(f) });
  
  

  Each file and directory will be passed to the filter to determine whether it will then be passed to the callback function. Like Array.filter does in JavaScript. There are three kinds of return values for filter function:

  • true: Will be passed to callback.
  • false: Will not be passed to callback.
  • skip: Same with false, and skip to watch all its subdirectories.

  On Linux, where the recursive option is not natively supported, it is more efficient to skip ignored directories by returning the skip flag:

  watch('./', {
    recursive: true,
    filter(f, skip) {
      // skip node_modules
      if (/\/node_modules/.test(f)) return skip;
      // skip .git folder
      if (/\.git/.test(f)) return skip;
      // only watch for js files
      return /\.js$/.test(f);
    }
  });
  
  

  If you prefer glob patterns you can use minimatch or picomatch together with filter:

  const pm = require('picomatch');
  let isMatch = pm('*.js');
  
  watch('./', {
    filter: f => isMatch(f)
  });
  

• delay: Number (in ms, default 200)

  Delay time of the callback function.

  // log after 5 seconds
  watch('./', { delay: 5000 }, console.log);
  

Events

The events provided by the callback function is either update or remove, which is less confusing to fs.watch's rename or change.

watch('./', function(evt, name) {

  if (evt == 'update') {
    // on create or modify
  }

  if (evt == 'remove') {
    // on delete
  }

});

Watcher object

The watch function returns a fs.FSWatcher like object as the same as fs.watch (>= v0.4.0).

Watcher events

let watcher = watch('./', { recursive: true });

watcher.on('change', function(evt, name) {
  // callback
});

watcher.on('error', function(err) {
  // handle error
});

watcher.on('ready', function() {
  // the watcher is ready to respond to changes
});

Close

// close
watcher.close();

// is closed?
watcher.isClosed()

List of methods

• .on
• .once
• .emit
• .close
• .listeners
• .setMaxListeners
• .getMaxListeners

Extra methods

• .isClosed detect if the watcher is closed
• .getWatchedPaths get all the watched paths

Known issues

Windows, node < v4.2.5

• Failed to detect remove event
• Failed to get deleted filename or directory name

MacOS, node 0.10.x

• Will emit double event if the directory name is of one single character.

Misc

1. Watch multiple files or directories in one place

watch(['file1', 'file2'], console.log);

2. Customize watch command line tool

#!/usr/bin/env node

// https://github.com/nodejs/node-v0.x-archive/issues/3211
require('epipebomb')();

let watcher = require('node-watch')(
  process.argv[2] || './', { recursive: true }, console.log
);

process.on('SIGINT', watcher.close);

Monitoring chrome from disk:

$ watch / | grep -i chrome

3. Got ENOSPC error?

If you get ENOSPC error, but you actually have free disk space - it means that your OS watcher limit is too low and you probably want to recursively watch a big tree of files.

Follow this description to increase the limit: https://confluence.jetbrains.com/display/IDEADEV/Inotify+Watches+Limit

Alternatives

• chokidar
• gaze
• mikeal/watch

Contributors

Thanks goes to all wonderful people who have helped this project.

License

MIT

Copyright (c) 2012-2021 yuanchuan