Javascript subclass doesnt inherit parent variable

Question

Javascript subclass doesnt inherit parent variable

I'm working with Javascript "classes", I have a parent "class" with a variable and a function, something like this

function WS() {
  this.auth = { client: '', password: '' };
  this.Execute = function(url, callback) {
    soap.createClient(url, function(err, client) {
      if (err) return callback(err);
      return callback(null, client);
    });
  }
}

The "subclass" uses this function and variable, like this

function Stats() {
  this.url = 'http://';

  this.emailsByDate = function(params, callback) {
    this.Execute(this.url, function(err, client) {
      if (err) return callback(err);
      client.Get(this.auth.concat(params), function(err, results) {
        if (err) return callback(err);
        return callback(results);
      });
    });
  }
}

Stats.prototype = new WS;

I'm getting through this.Execute() function, but this.auth variable is undefined, why is that

javascript
node.js

Answer 1

The context in which you are accessing this.auth isn't your Stats function, but instead your anonymous callback function.

You could either save the value of this.auth outside the callback function:

function Stats() {
  var auth = this.auth
  this.url = 'http://';

  this.emailsByDate = function(params, callback) {
    this.Execute(this.url, function(err, client) {
      if (err) return callback(err);
      client.Get(auth.concat(params), function(err, results) {
        if (err) return callback(err);
        return callback(results);
      });
    });
  }
}

Or you can bind the context of your callback function to that of your Stats function:

function Stats() {
  this.url = 'http://';

  this.emailsByDate = function(params, callback) {
    this.Execute(this.url, function(err, client) {
      if (err) return callback(err);
      client.Get(this.auth.concat(params), function(err, results) {
        if (err) return callback(err);
        return callback(results);
      });
    }.bind(this));
  }
}