Creating your own event emitter object

We can create event emitters ourselves. This is even supported by Node.js by inheriting from the built-in events.EventEmitter class. But let's first implement a simple event emitter from scratch, because this explains the pattern in all its details.

For this, we are going to create a module whose purpose is to regularly watch for changes in the size of a file. Once implemented, it can be used like this:

'use strict';

watcher = new FilesizeWatcher('/path/to/file');

watcher.on('error', function(err) {
  console.log('Error watching file:', err);
});

watcher.on('grew', function(gain) {
  console.log('File grew by', gain, 'bytes');
});

watcher.on('shrank', function(loss) {
  console.log('File shrank by', loss, 'bytes');
});

watcher.stop();

As you can see, the module consists...