chapter.of: Extended Persistence
created: 20140708084614887
modified: 20140715184930403
sub.num: 2
tags: doc
title: Saver

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

<dl>
<dt>save</dt> <dd>This method is used, when the user requests a save, for example by clicking the save button in the sidebar.</dd>
<dt>autosave</dt> <dd>This method is used automatically by TW when tiddlers are changed, created or deleted by the user.</dd>
<dt>download</dt> <dd>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.</dd>
</dl>

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.