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Extended Persistence

17th July 2014 at 6:11pm

The microkernel only contains a bare store and some deserializers to load tiddlers from JSON files or from the DOM of the current HTML file. The core plug-in adds some more deserializers and a new mechanism for persisting and synchronising tiddlers.

This mechanism is provided as a global module in $:/core/modules/syncer.js. The saver module has three responsibilities:

  1. Save the whole wiki.
  2. Provide the ability to download single tiddlers as files.
  3. Synchronise the local wiki store with a remote wiki store, i.e. running in Node.js

The syncer module is connected mainly to two other modules. For one it registers to changes at the wiki store (Event Mechanism) and if any changes occur they are synced to the remote store. Then it provides a function saveWiki(options). This function can be used by other modules. For example the RootWidget uses this function to save the whole wiki or start downloading single tiddlers.

The syncer itself does not provide a concrete implementation of saving, downloading or syncing the tiddlers. Instead it loads modules of type saver and syncadaptor and manages the saving/syncing process.


Modules with module-type: tiddlerdeserializer can provide functions to create tiddlers out of any textual representation. Each function must be associated with a type like application/json or text/html. They get the textual representation of the tiddlers, some default field values and the type of the text block as arguments. They return an array of JavaScript objects representing the resulting tiddlers.

Deserializers are not managed by the syncer module. Instead the concept of deserializers is in fact part of the microkernel. This is necessary because the microkernel needs a way of loading tiddlers before it can load the core plug-in and execute it's startup modules. (Due to the fact that the core plug-in and it's modules are represented as tiddlers.)

The load-modules startup module loads additional deserializers and pushes them into the store. The core plug-in for example contains a few deserializers which can read a whole TiddlyWiki 5 or classic HTML file and load the individual tiddlers into the store.


Modules with module-type: saver provide functionality to save the whole wiki. There are three methods a saver can support:

This method is used, when the user requests a save, for example by clicking the save button in the sidebar.
This method is used automatically by TW when tiddlers are changed, created or deleted by the user.
This message is used when the wiki or a single tiddler should explicitly be downloaded. The control panel for example uses this method to provide a button which saves the wiki as a static HTML file.

A saver module has to export two functions. canSave(wiki) returning true if this module is capable of working and create(wiki) returning an instance of a saver object. This saver object has to provide an info property containing a name, a priority, an array of methods it supports and a method save(text,method,callback). This method is called from TW with the actual text which should be saved, the method which is used and a callback function to report errors: callback("Error while saving") or to notify that saving went well: callback(null, "Saving went well :)"). If the saver method successfully saved the file it has to return true, or false otherwise. Saves are triggered by messages from the UI. The syncer module uses the saver with the highest priority capable of the requested method to save the file.

The core plug-in contains a saver capable of saving the current state of the wiki to the local hard drive by using a special Firefox extension called Tiddlyfox. If this extension is not available, the savers canSave method would return false. A saver with a lower priority would then ask the user to save the current state as a new HTML file.


A module with module-type: syncadaptor provides functionality to get a list of tiddlers (this list is provided as SkinnyTiddlers, which are normal tiddlers without the text field) and to load, save and delete single tiddlers. A syncadaptor can also provide functions to login and logout so that syncadaptor modules can be used to synchronize tiddlers with a remote server.

The syncer module only uses one syncadaptor and honours a special system tiddler $:/config/SyncFilter containing a filter string. Tiddlers matching this filter string are not saved to the server with a syncadapter. It uses the WebServer API to load modified tiddlers from the server, which returns only non-system tiddlers.