title: PluginMechanism
tags: internals

!Introduction

TiddlyWiki5 is based on a 500 line boot kernel that runs on node.js or in the browser, and everything else is plugins.

The kernel boots just enough of the TiddlyWiki environment to allow it to load tiddlers as plugins and execute them (a barebones tiddler class, a barebones wiki store class, some utilities etc.). Plugin modules are written like `node.js` modules; you can use `require()` to invoke sub components and to control load order.

There are several different types of plugins: parsers, serializers, deserializers, macros etc. It goes much further than you might expect. For example, individual tiddler fields are plugins, too: there's a plugin that knows how to handle the `tags` field, and another that knows how to handle the special behaviour of
the `modified` and `created` fields.

Some plugins have further sub-plugins: the wikitext parser, for instance, accepts rules as individual plugins.

!Plugins and Modules

In TiddlyWiki5, a plugin is a bundle of related tiddlers that are distributed together as a single unit. Plugins can include tiddlers which are JavaScript modules. 

The file `core/boot.js` is a barebones TiddlyWiki kernel that is just sufficient to load the core plugin modules and trigger a startup plugin module to load up the rest of the application.

The kernel includes:

* Eight short shared utility functions
* Three methods implementing the plugin module mechanism
* The `$tw.Tiddler` class (and three field definition plugins)
* The `$tw.Wiki` class (and three tiddler deserialization methods)
* Code for the browser to load tiddlers from the HTML DOM
* Code for the server to load tiddlers from the file system

Each module is an ordinary `node.js`-style module, using the `require()` function to access other modules and the `exports` global to return JavaScript values. The boot kernel smooths over the differences between `node.js` and the browser, allowing the same plugin modules to execute in both environments.

In the browser, `core/boot.js` is packed into a template HTML file that contains the following elements in order:

* Ordinary and shadow tiddlers, packed as HTML `<DIV>` elements
* `core/bootprefix.js`, containing a few lines to set up the plugin environment
* Plugin JavaScript modules, packed as HTML `<SCRIPT>` blocks
* `core/boot.js`, containing the boot kernel

On the server, `core/boot.js` is executed directly. It uses the `node.js` local file API to load plugins directly from the file system in the `core/modules` directory. The code loading is performed synchronously for brevity (and because the system is in any case inherently blocked until plugins are loaded).

The boot kernel sets up the `$tw` global variable that is used to store all the state data of the system.

!Core 

The 'core' is the boot kernel plus the set of plugin modules that it loads. It contains plugins of the following types:

* `tiddlerfield` - defines the characteristics of tiddler fields of a particular name
* `tiddlerdeserializer` - methods to extract tiddlers from text representations or the DOM
* `startup` - functions to be called by the kernel after booting
* `global` - members of the `$tw` global
* `config` - values to be merged over the `$tw.config` global
* `utils` - general purpose utility functions residing in `$tw.utils`
* `tiddlermethod` - additional methods for the `$tw.Tiddler` class
* `wikimethod` - additional methods for the `$tw.Wiki` class
* `treeutils` - static utility methods for parser tree nodes 
* `treenode` - classes of parser tree nodes
* `macro` - macro definitions
* `editor` - interactive editors for different types of content
* `parser` - parsers for different types of content
* `wikitextrule` - individual rules for the wikitext parser
* `command` - individual commands for the `$tw.Commander` class

TiddlyWiki5 makes extensive use of JavaScript inheritance:

* Tree nodes defined in `$:/core/treenodes/` all inherit from `$:/core/treenodes/node.js`
* Macros defined in `$:/core/macros/` all inherit from `$:/core/treenodes/macro.js`

`tiddlywiki.plugin` files