Utilising Nodejs Promises (Bluebird) during module loading and configuration - node.js

Question

Morning All
I've been scouring S.O. for the past couple of days trying to find an answer I understood/was applicable to my situation, and have now admitted defeat, primarily due to my lack of comprehension around Promises (promise-n00b). So I'm basically putting out a plea for some help with my example posted below. I think it's fairly explanatory what I'm doing but in case it isn't, I'm trying to:
Apply some synchronous config to the server
Load a Logger module and instantiate a new of instance of it as logger, and then run some necessary checks (e.g. do we have a log file?) before returning an indicator to say that it loaded successfully (either a boolean or the logger object itself)
Then pass that logger to the utils (they need it to log)
Finally call the callback passed in by the scripts run by npm start and npm test
Obviously there's a lot more going on in the real world but I'd tried to distil the code down to the bit I don't get, namely the Promise chain.
Finally, as a long term user of callbacks who has never struggled to comprehend them (brain must work differently perhaps) do any of you dudes have any pearls of wisdom likely to cause a lightbulb moment?
Many thanks in advance and yes I know this code as it stands doesn't/won't work ;-)
Code as follows:
server.js
var Promise = require('bluebird');
var fs = Promise.promisifyAll(require('fs-extra'));
var boss = {
start: function(callback) {
var p = new Promise.try(function() {
console.log('start');
})
.then(boss.applyConfig)
.then(boss.startLogger)
.then(function(lggr) {
console.log('logger setup complete: ' + lggr);
boss.logger = lggr;
return lggr;
})
.then(boss.loadUtils)
.finally(function() {
if (callback) callback();
})
.catch(function(err) {
console.log.call(null, '\033[31m' + err.stack + ' \033[39m');
});
},
applyConfig: function() {
console.log('applying config');
return 'config';
},
startLogger: function() {
console.log('starting logger');
var Logger = require('./Logger')(fs, Promise);
var logger = new Logger();
return new Promise(function(resolve, reject) {
var result = logger.init();
if (result) {
resolve(logger);
}
else {
reject(logger);
}
});
},
loadUtils: function(logger) {
console.log('loading utils with ' + logger);
boss.logger.log('loading utils with ' + logger);
return 'utils';
}
};
boss.start(function(){
console.log('done');
});
Logger.js
module.exports = function(fs, Promise) {
var Logger = function(options) {
this.filePath = (options && options.filePath) ? options.filePath : __dirname + '/../log/';
this.filename = (options && options.filename) ? options.filename : 'all.log';
};
Logger.prototype.init = function() {
var logger = this;
console.log('logger.init');
return new Promise(function(resolve) {
new Promise.resolve(logger.checkForLogFile()).then(function(exs) {
console.log('exs', exs);
return exs;
});
})
};
Logger.prototype.log = function(msg) {
// requires that the log file exists and that we have a stream to it (create stream function removed)
console.log.call(null, '\033[36mLogging: ' + msg + ' \033[39m');
};
Logger.prototype.checkForLogFile = function() {
var logger = this;
fs.existsAsync(logger.filePath + logger.filename).then(function (exists) {
console.log('exists', exists);
return exists;
});
};
return Logger;
};

Answer 1

First up - thanks Benjamin :) And secondly, how amazingly surprising that all this would now work within 30 mins of posting on S.O. after a couple of days prior effort ;-)
So yes - golden takeaway nugget is KISS!
Following code now works correctly and logs in the correct order as follows:
start
applying config
starting logger
logger.init
statObj { dev: 2067,
mode: 33204,
...
ctime: Thu Nov 27 2014 11:40:34 GMT+0000 (GMT) }
exists true
logger setup complete: [object Object]
loading utils with [object Object]
Logging: loading utils with [object Object]
done
server.js
var Promise = require('bluebird');
var fs = Promise.promisifyAll(require('fs-extra'));
var boss = {
start: function(callback) {
var p = new Promise.try(function() {
console.log('start');
})
.then(boss.applyConfig)
.then(boss.startLogger)
.then(function(lggr) {
console.log('logger setup complete: ' + lggr);
boss.logger = lggr;
return lggr;
})
.then(boss.loadUtils)
.finally(function() {
if (callback) callback();
})
.catch(function(err) {
console.log.call(null, '\033[31m' + err.stack + ' \033[39m');
});
},
applyConfig: function() {
console.log('applying config');
return 'config';
},
startLogger: function() {
console.log('starting logger');
var Logger = require('./Logger')(fs, Promise);
var logger = new Logger();
return logger.init();
},
loadUtils: function(logger) {
console.log('loading utils with ' + logger);
boss.logger.log('loading utils with ' + logger);
return 'utils';
}
};
boss.start(function(){
console.log('done');
});
Logger.js
module.exports = function(fs, Promise) {
var Logger = function(options) {
this.filePath = (options && options.filePath) ? options.filePath : __dirname + '/../log/';
this.filename = (options && options.filename) ? options.filename : 'all.log';
};
Logger.prototype.init = function() {
var logger = this;
console.log('logger.init');
return logger.checkForLogFile().then(function(statObj) {
var exists = (typeof statObj === 'object');
console.log('exists', exists);
return logger;
});
};
Logger.prototype.log = function(msg) {
// requires that the log file exists and that we have a stream to it (create stream function removed)
console.log.call(null, '\033[36mLogging: ' + msg + ' \033[39m');
};
Logger.prototype.checkForLogFile = function() {
var logger = this;
return fs.statAsync(logger.filePath + logger.filename).then(function (statObj) {
console.log('statObj', statObj);
return statObj;
});
};
return Logger;
};