Overview

The heart of TiddlyWiki can be seen as an extensible representation transformation engine. Given the text of a tiddler and its associated ContentType, the engine can produce a rendering of the tiddler in a new ContentType. Furthermore, it can efficiently selectively update the rendering to track any changes in the tiddler or its dependents.

The primary use of the engine is to convert raw text/vnd.tiddlywiki WikiText into a text/html or text/plain representation for display. The transclusion and templating features of WikiText allow the engine to also be used to generate TiddlyWiki HTML files from raw tiddlers.

You can explore this mechanism by opening the JavaScript console in your browser. Typing this command will replace the text of the tiddler HelloThere with new content:

$tw.wiki.addTiddler({title: "HelloThere", text: "This is some new content"});

If the tiddler HelloThere is visible then you'll see it instantly change to reflect the new content. If you create a tiddler that doesn't currently exist then you'll see any displayed links to it instantly change from italicised to normal:

$tw.wiki.addTiddler({title: "TiddlyWiki5", text: "This tiddler now exists"});

If you're interested in understanding more about the internal operation of TiddlyWiki, it is recommended that you review the Docs and read the code – start with the boot kernel $:/core/boot.js.

Introduction

TiddlyWiki5 is based on a 1,000 line boot kernel that runs on node.js or in the browser, with all other functionality added via dynamically loaded modules.

The kernel boots just enough of the TiddlyWiki environment to allow it to load tiddlers and execute JavaScript modules. Plugin modules are written like node.js modules.

There are many different types of module: parsers, serializers, deserializers, macros etc. It goes much further than you might expect. For example, individual tiddler fields are modules, too: there's a module 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 plugin modules have further sub-plugins: the wikitext parser, for instance, accepts rules as individual plugin modules.

Plugins and Modules

In TiddlyWiki5, Plugins are bundles of tiddlers that are distributed and managed as one; Modules are JavaScript tiddlers with a module type identifying when and how they should be executed.

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

The kernel includes:

• Several short shared utility functions
• A handful of methods implementing the plugin module mechanism
• The $tw.Tiddler class (and field definition plugins)
• The $tw.Wiki class (and 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
• 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.