An extension-point based open plugin framework
This module is an extension-point based framework for loading plugins, inspired by Eclipse plugin system.
The scenario can explain why this module is developed:
Developer A made an excellent text editor which can be installed using
npm install xedit -g
Developer B is a language expert and he invents a new language.
He loves xedit so much that he wants to make a plugin for it.
A few days later, he published a module called
User simply use
npm install xedit -gnpm install xedit-lang-x -g
than, xedit automatically recognized language x.
In the scenario above, xedit scans and loads plugins.
In this way, xedit is called host in this framework.
And xedit-lang-x is a plugin.
A host will require js-plugins to manage plugins,
while a plugin doesn't require js-plugins but need a special section in
package.json to describe what the plugin provides.
Here's an example what xedit-lang-x written in the
In the example above, section
extensions defines what extensions are provided by this module.
The key of the hash is the extension-point name,
and the value can be a path to the actual script file or a name representing an attribute from the object provided by
When xedit starts, it uses js-plugins to scan all installed modules and find out all available extensions from
When it is going to load a language plugin, it uses extension-point name
xedit:language to load all matched extensions.
By default, js-plugins scans the following locations in sequence (latter ones may override former ones):
js-plugins provides a simple class
var Plugins = require'js-plugins';var pluginManager = ;
pluginManager, we can
pluginManagerregisterextensionPoint name factory;
to register a plugin mapped to
factory is defined in two forms distinguished by the number of arguments:
; // the async version, the extension is created asynchronously// callback is defined as function callback(err, extension); // the sync version, the extension is returned directly
Factories with argument number less than 3 are treated as sync version. The parameters are defined as:
data: opaque data which is recognized by host and plugin
host: instance of host
options: additional information, currently defined
extensionPoint: name of extension-point
name: name of extension
callback: for receiving the extension, in the form of
function (err, extension)
pluginManagerconnecthost extensionPoint options callback
The parameters are defined as:
host: the host instance
extensionPoint: name of extension-point
options: a hash defined as
data: passed to extension factory as the first argument
multi: when true, connect all available extensions registered to the same extension-point, when false, the first extension is connected
name: when is a string, explicitly specify the name of the extension, when is an array, names are iterated until an extension is connected
required: when true, error is thrown if no extensions found
callback: defined as
function (err, extensions), it is possible
extenionsis a single instance or an array when
dirs is an array of directories, under each the first level sub-directories are scanned for
It scans all default directories in the sequence described above. The latter modules may override the former ones if the same extension-point + name is registered.
Plugins provides a global instance which can be accessed using
All methods are promoted under
Plugins directly. E.g.
Plugins.scan is equivalent to
Plugins.instance.scan. The recommended practise is to use the global instance as much as possible, and invoke
Plugins.scan once at application start-up.
js-plugins is not needed. The only thing to do is presenting
extensions section in
extensions section is a hash with each key as an extension-point, and the value is also another hash
with each key as extension name. The value can be in several form:
- hash: this is the complete form, it defines 2 attributes:
module: if present, specify the path of script file which will be loaded using
require, otherwise the top directory (containing
package.json) is required;
object: when present, it means the required module doesn't provide a factory directory, but must use the value of
objectto get the factory
- string without '/': equals to hash form without
- string with '/': equals to hash form with
See above to find out how to define a factory.