Simple engine for creating plugin-driven applications

First, instantiate a plugin manager:

var PluginManager = require('fireplug');
var plugins = new PluginManager();

Next, start using plugins:

var pluginA = {
  method1: function(prev, param1, param2, cb) {
    cb(null, someValue);
  },
  method2: function(prev, param1) {
    return somePromise;
  }
};

var pluginB = {
  method2: function(prev, param1) {
    return prev;
  }
};

plugins.use(pluginA);
plugins.use(pluginB);
plugins.use(arrayOfPlugins);

A plugin is an object with methods. The methods each take, as their first parameter, the value (if any) from any previous plugin, additional parameters for the method, and a callback parameter. The plugin method can work synchronous by either:

• Returning the previous result argument
• Returning null
• Returning a regular value
• Throwing an error

...or asynchronously by:

• Calling a node-style callback argument
• Returning a promise

To invoke plugins, you call the method through the plugin manager in one of two ways, through invoke:

plugins
  .invoke('method1', arg1)
  .then(
    function(result) {
      // Handle result
    },
    function(err) {
      // Handle error
    });

...or, if you know a method is defined at least one plugin, you can use the method name directly:

plugins
  .method1(arg1)
  .then(
    function(result) {
      // Handle result
    },
    function(err) {
      // Handle error
    });

In either case, the plugins are invoked asynchronously so that the plugin author always have an asynchronous option. fireplug uses Promises/A+.

The suggested strategy for structuring a plugin-based application is to integrate a built-in set of plugins, then enable a consumer of your application to inject additional plugins.