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POAsynchronous initialization of Node.js module
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copied!<p>I'd like to initialize module in asynchronous way and come up with couple of ideas. I need DB object with list of collections from Mongo and other data, but list of files in <code>./</code> will do for brevity.</p> <p>I can't export function or class because I need <code>require('db')</code> to return same object everytime.</p> <hr/> <p><strong>First</strong> and simplest what came to my mind is to assign <code>module.exports</code> to <code>Object</code> and populate it later:</p> <pre class="lang-js prettyprint-override"><code>var exports = {}; module.exports = exports; require('fs').readdir('.', function(err, files) { exports.error = err; exports.files = files; }); </code></pre> <p>Bad thing — I don't really know from outside when list is ready and no good way to check for errors.</p> <hr/> <p><strong>Second</strong> way I've comed up with is to inherit <code>EventEmitter</code> and notify everyone that DB is ready or error occured. If everything ok - keep going.</p> <pre class="lang-js prettyprint-override"><code>var events = require('events'); var util = require('util'); function Db() { events.EventEmitter.call(this); this.ready = false; this.files = null; this.initialize(); } util.inherits(Db, events.EventEmitter); Db.prototype.initialize = function() { if (this.ready) return this.emit('ready'); var self = this; require('fs').readdir('.', function(err, files) { if (err) return self.emit('error', err); self.files = files; self.ready = true; self.emit('ready'); }); }; module.exports = new Db(); </code></pre> <hr/> <p>And <strong>now</strong> I think that's more reasonable:</p> <pre class="lang-js prettyprint-override"><code>// db.js var exports = {init: init}; module.exports = exports; function init(callback) { callback = (typeof callback === 'function') ? callback : function() {}; require('fs').readdir('.', function(err, files) { delete exports.init; exports.result = files; // that's pretty much what I need, // so don't mind result slightly differs // from previous cases callback(err); }); } </code></pre> <pre class="lang-js prettyprint-override"><code>// main.js var db = require('./db'); // check for `db.init` presence maybe... db.init(function(err) { return err ? console.error('Bad!') : console.log(db); // It works! }); </code></pre> <hr/> <p>What should I pick and why? How bad is such idea in general and my options in particular?</p> <p>Thanks for feedback.</p>

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