Buffer.ceylon

shared dynamic Buffer {
	
}

FS.ceylon

import io.nodejs.buffer { Buffer }

dynamic FS {
	
	"Asynchronously append data to a file, creating the file if it not yet 
	 exists. data can be a string or a buffer.
	 
	 JS example:
	 	fs.appendFile('message.txt', 'data to append', function (err) {
	 		if (err) throw err;
	 		console.log('The \"data to append\" was appended to file!');
	 	});
	 
	 The `options` object can have these three options:
	 * `encoding` String | Null default = 'utf8'
	 * `mode` Number default = 438 (aka 0666 in Octal)
	 * `flag` String default = 'a'"
	shared formal void appendFile(String filename, String|Buffer data, Object? options, Callable<Object, [Anything]> callback);
	
	"The synchronous version of [[FS.appendFile]]"
	shared formal void appendFileSync(String filename, String|Buffer data, Object? options);
	
}

FS requireFS() {
	dynamic { return require("fs"); }
}

I would leave options as dynamic instead of Object?. Not sure about the signature of callback.

Sweet! I'm on the right track then! Thanks for the speedy reply!