Subclassing well-behaved modules

You can subclass any well-behaved module, in much the way you would subclass snippets.

We've made subclassing easier for the common case where you want to change the behavior of an existing module for this particular project. Just create an index.js file in your lib/modules/mymodulename folder, where mymodulename is the full name of the npm module you're subclassing.

Here's a really simple subclass that changes the way the index method of the apostrophe-blog module behaves, so that a featured story is available to the index.html template as the featured variable in nunjucks:

module.exports = stories;

function stories(options, callback) {
  return new stories.Construct(options, callback);
}

stories.Construct = function(options, callback) {
  var self = this;

  module.exports.Super.call(this, options, null);

  var superIndex = self.index;
  self.index = function(req, snippets, callback) {
    self.get(req, { tags: 'featured' }, { limit: 1 }, function(err, results) {
      if(err) {
        callback(err);
      }
      if(results.total > 0) {
        req.extras.featured = results.snippets[0];
      }
      superIndex(req, snippets, callback);
    });
  };

  // Must wait at least until next tick to invoke callback!
  if (callback) {
    process.nextTick(function() { return callback(null); });
  }

};

Note the use of module.exports.Super. This automatically points to the base class constructor.

Confused? Just remember to follow this pattern and place your method overrides after the call to module.exports.Super.

Apostrophe follows the "self pattern," rather than the prototype pattern. Those who are used to implementing inheritance with the prototype keyword will find it slightly different. We prefer this pattern because it eliminates several common sources of bugs.