node-style.js

obj.method(arg, options, function(err, value){
	
	if (err) {
		// handle or rethrow
	}
	
	doSomethingWith(value);
	
});

// alternative to promise-ify (with Q)
Q.ninvoke(obj, "method")
	.then(function(value){
		doSomethingWith(value)
	})
	.fail(function(err){
		// handle or rethrow
	})
	.done();
	
// if you want to use promises inside your lib, you can also do this
obj.method = function(args, options, cb)
{
	// do whatever you need to do
	
	return Q.resolve(value).nodeify(cb);
}

// to use the above, one can go simple callback style, i.e. exactly as the very first example here
obj.method(args, options, function(e, v){ /* same as first example */ });

// or one can directly use the promises API like this:
obj.method(args, options)
	.then(function(v){ /* do stuff */ })
	.fail(function(e){ /* handle stuff */ })
	.done();
	
// promises FTW!