Promise.promisifyAll of a class and errors

output withErrors=false

start promisifyInLine
calling `a`, willError=false
promisifyInLine from a=123
calling `b`, willError=false
promisifyInLine from b=456
promisifyInLine error=null results=done promisifyInLine

start promisifyUsingAll
calling `a`, willError=false
promisifyUsingAll from a=123
calling `b`, willError=false
promisifyUsingAll from b=456
promisifyUsingAll error=null results=done promisifyUsingAll

Done.

output withErrors=true

start promisifyInLine
calling `a`, willError=true
Error in promisifyInLine. msg=Bad thing happened in a.
promisifyInLine error=Error: Bad thing happened in a. results=undefined

start promisifyUsingAll
calling `a`, willError=true
Error in promisifyUsingAll. msg=Bad thing happened in a.
promisifyUsingAll error=Error: Bad thing happened in a. results=undefined

Done.

promise.js

'use strict';
var Promise = require('bluebird');
var async = require('async');
var willError = false;

function SomeClass() {

}
SomeClass.prototype.a = function (callback) {
	console.log('calling `a`, willError=' + willError);
	if (willError) {
		callback(new Error('Bad thing happened in a.'));
		return;
	}
	callback(null, '123');
};

SomeClass.prototype.b = function (callback) {
	console.log('calling `b`, willError=' + willError);
	if (willError) {
		callback(new Error('Bad thing happened in b.'));
		return;
	}
	callback(null, '456');
};

Promise.promisifyAll(SomeClass.prototype);

function promisifyInLine(callback) {
	console.log('start promisifyInLine');
	var myClass = new SomeClass();
	Promise.promisify(myClass.a, myClass)()
		.then(function (aResults) {
			console.log('promisifyInLine from a=' + aResults);
			return Promise.promisify(myClass.b, myClass)();
		})
		.then(function (bResults) {
			console.log('promisifyInLine from b=' + bResults);
			callback(null, 'done promisifyInLine');
		})
		.catch(function (error) {
			console.log('Error in promisifyInLine. msg=' + error.message);
			callback(error);
		});
}

function promisifyUsingAll(callback) {
	console.log('start promisifyUsingAll');
	var myClass = new SomeClass();
	myClass.aAsync()
		.then(function (aResults) {
			console.log('promisifyUsingAll from a=' + aResults);
			return myClass.bAsync();
		})
		.then(function (bResults) {
			console.log('promisifyUsingAll from b=' + bResults);
			callback(null, 'done promisifyUsingAll');
		})
		.catch(function (error) {
			console.log('Error in promisifyUsingAll. msg=' + error.message);
			callback(error);
		});
}


async.series([
	function (seriesCb) {
		console.log('');
		promisifyInLine(function (error, results) {
			console.log('promisifyInLine error=' + error + ' results=' + results);
			seriesCb(); //ignoring errors to progress series
		})
	},
	function (seriesCb) {
		console.log('');
		promisifyUsingAll(function (error, results) {
			console.log('promisifyUsingAll error=' + error + ' results=' + results);
			seriesCb(); //ignoring errors to progress series
		})
	}
], function () {
	console.log('');
	console.log('Done.');
	process.exit(0);
})