44 lines
2.9 KiB
Plaintext
44 lines
2.9 KiB
Plaintext
created: 20130825142900000
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modified: 20140502142900000
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tags: Mechanisms
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title: BootMechanism
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type: text/vnd.tiddlywiki
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!Introduction
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At its heart, TiddlyWiki5 is a relatively small boot kernel that runs either under Node.js or in the browser with all other functionality added via dynamically loaded [[modules|Modules]].
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The kernel boots just enough of the TiddlyWiki environment to allow it to load and execute module tiddlers. The module system is compatible with CommonJS and [[Node.js]].
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There are many [[different types of module|ModuleType]]: parsers, deserializers, widgets 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 parsing rules as individual plugin modules.
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!Plugins
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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.
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The tiddler [[$:/boot/boot.js]] is a barebones TiddlyWiki kernel that is just sufficient to load the core plugin modules and trigger a startup module to load up the rest of the application.
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The boot kernel includes:
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* Several short shared utility functions
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* A handful of methods implementing the module mechanism
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* The `$tw.Tiddler` class (and field definition plugins)
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* The `$tw.Wiki` class (and tiddler deserialisation methods)
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* Code for the browser to load tiddlers from the HTML DOM
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* Code for the server to load tiddlers from the file system
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Each module is an ordinary CommonJS module, using the `require()` function to access other modules and the `exports` global to return JavaScript values. The boot kernel smooths over the differences between `Node.js` and the browser, allowing the same plugin modules to execute in both environments.
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In the browser, `core/boot.js` is packed into a template HTML file that contains the following elements in order:
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* Ordinary and system tiddlers, packed as HTML `<DIV>` elements
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* `core/bootprefix.js`, containing a few lines to set up the plugin environment
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* Optional JavaScript modules, packed as HTML `<SCRIPT>` blocks
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* `core/boot.js`, containing the boot kernel
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On the server, `core/boot.js` is executed directly. It uses the `Node.js` local file API to load plugins directly from the file system in the `core/modules` directory. The code loading is performed synchronously for brevity (and because the system is in any case inherently blocked until plugins are loaded).
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The boot process sets up the `$tw` global variable that is used to store all the state data of the system.
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At the end of the boot process the StartupMechanism schedules the execution of startup modules to bring up the rest of TiddlyWiki.
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