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I'm having a lot of trouble trying to modify a "this" object from within a pseudo javascript class when it's already been initialized

I'm having a lot of trouble trying to modify a "this" object from within a pseudo javascript class when it's already been initialized


Scroll down to the bottom of this post to see a work around / possible solution.

This is probably easier just to explain in the source Code with comments. The issue at hand is I cannot figure out how pseudo classes work together to perform the task I'm trying to do (explained in the code below).

The code is broken down into 3 files: lead.js, router.js, and db.js.

There are a decent amount of lines of code but most of it is comments.


var bcrypt = require('bcrypt'),
    validators = require('../lib/validators'),
    utility = require('../lib/utility'),
    document = {};

var Lead = module.exports = function (db) {
  // Save a reference to the database.
  this.db = db;

  // Reference initial document.
  // This is totally wrong, not sure how to 'send' a variable to the constructor of a class
  // when I cannot add another param. Due to how I'm importing the db model, I won't know what
  // the document is until I fill out the form. I've also tried 'document' instead of 'Lead.document'.
  this.document = Lead.document;

  // Setup the document if it exists.
  // This also doesn't work.
  // Basically I want to be able to set up a document variable outside of this module (line #100),
  // Then pass it to this module after filling it up with values from a form.
  // Then based on what's been filled in, it would fix up (trim, convert to lower case)
  // some of the values automatically and default a few values that I'm not always going to pass.
  if (!document) {
    var salt = bcrypt.genSaltSync(10),
        hash = bcrypt.hashSync(utility.generatePassword(), salt);

    // Default values.
    if (!document.meta.createdAt) { this.document.meta.createdAt =; }
    if (!document.login.password) { this.document.login.password = hash; }
    if (!document.login.role) { this.document.login.role = 'User'; }

    // Normalize a few values. =; =; =; =; =; =; =; =;
  // So in regards to the above code, the end result I'm looking for is...
  // I want to append some properties to the this.document reference when the document is empty (when I'm updating it, I won't set the document), 
  // and on new documents it will append a few default values/normalize all the fields.

Lead.prototype.validate = function(fn) {
  var errors = [];

  // Some validation rules I cut out to make this shorter.

  if (errors.length) return fn(errors);
}; = function(fn) {
  this.db.collection('leads', function(err, collection) {
    if (err) { fn(new Error({message: err})); }

    collection.insert(this.document, function(err, result) {
      return fn(err, result);


[route.js file]

  var db = require('../models/db');'/register', function(req, res) {
    var data = req.body.lead || {};

    // Fill the document.
    var document = {
      meta: {
        referer: req.headers.referer,
        createdIPAddress: req.connection.remoteAddress
      login: {
      contact: {
        name: {
          first: data.first,
          last: data.last
        address: {
          street: data.street,
          state: data.state,
        phone: {

    // Write the document.
    db.lead.document = document;

    db.lead.validate(function(err) {
      if (err) {
        req.session.error = err;
        return res.redirect('back');
      } {


var mongodb = require('mongodb'),
    server = new mongodb.Server('localhost', 27017),
    connection = new mongodb.Db('test', server);, db) {});

module.exports =  {
  lead: new (require('./lead'))(connection)

When I run this, my validator always reports that the password is empty which makes sense. I'm sending the Document initially to the class with an empty password (the password is randomly generated, not a form field) -- the problem is I have no idea what to do with the if (!document) ... code block to actually set the this.document properly.

I hope between the comments and code you can get an idea of what I'm trying to do. I've been stuck on this for a while.


I changed the flow of it a bit to get a solution.

In the db.js, I exported the connection rather than instantiating the lead (and future models) directly.

In the router.js file, I require the db and lead file, then pass both the db connection and the document in the constructor of the Lead. Ex.

var lead = new Lead(db, document);

In the lead.js file, it becomes as simple as doing this.document = document (same as the db). When I submit a new lead, the values I don't send over from router.js get appended to the document (the created date, a random password, etc.) and everything is good.

Is this a decent way of handling this, or is there a better way to refactor this?

Problem courtesy of: AntelopeSalad


You need to read up on object-oriented programming in Javascript.

The anonymous function you're defining near the top of your code is the constructor function, so with respect to the document property you want that is currently uninitialized, just type something like:

this.document = null;

Then some time later when you create a new object using this constructor, like so:

var myLead = new Lead(dbConnection);

You'll have the myLead.document property.

There are many other things wrong with your code, though. Why are you assuming that there is a global document variable with relevant data visible in your library when it's defined as {}? The code in that if statement at the end of your constructor should be run when the document property is set in your other file below, and should only expect this.document to exist.

Solution courtesy of: David Ellis


View additional discussion.

This post first appeared on Node.js Recipes, please read the originial post: here

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I'm having a lot of trouble trying to modify a "this" object from within a pseudo javascript class when it's already been initialized


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