proto.dot

digraph smtp {
  init -> A [label=greet];
  A -> done [label=ehlo];
}

proto.js

const patterns = {
	init_greet : (q, data) => {
		data
			.command('EHLO ...')
			.done(q => q.resolve('A'))
	}
	A_ehlo : (q, data) => {
		q.resolve('done')	
	}
}

function handle(q, state, event, data)
{
	const k = state + _ + event;
	if (k in patterns)
	{
		patterns[k](q, data)
	}
	else
	{
		q.resolve('done')
	}
}