Safe Scripted Transclusions for TiddlySpace

I propose a new feature to TiddlyWiki to allow users to write scripted transclusions in a way that can be safely shared. Scripted transclusions are designed as a safe way to satisfy some of the popular use cases for unsafe features like plugins and evaluated macro parameters discussed in SecurityHandling.

Scripted transclusions are not intended to replace plugins; systemConfig plugins will still be needed as the means to modify TiddlyWiki itself.

Scripted transclusions are called in the same way as ordinary ones:

<<tiddler MyTransclusion with:Param1 Param2>>

Scripted transclusions kick in if the target tiddler is tagged systemScript. Instead of the text of the target tiddler being transcluded, the text is executed as a safe subset of JavaScript, and the value that it returns is wikified as the result of the <<tiddler>> macro.

systemScript tiddlers are executed as if they were wrapped in the following:

return (function ($$,tiddler,script) {
// systemScript tiddler body goes here
})($$,tiddler,script);

One approach to implementing the safe subset of JavaScript is parse the script to a tree representation that can then be compiled to JavaScript. If necessary, runtime checks can be incorporated by, for example, compiling a = b; to safeAssign(a,b);.

Observations and reservations:

• The parameters passed to the script should include:
  • the parameters passed to the transclusion
  • the tiddler that called the transclusion
  • the script that is executing
  • the tiddler store
  • the story, represented as an array of objects
  • regular expression functionality
  • runtime information, such as:
    • the current date and time
    • the current URL
    • the current username
• Rather than using the existing <<tiddler>> macro, it may be preferable to introduce a new syntax, such as [[[MyScript]]], or [[[MyScript param:one param2:two]]]
• Should we allow access to the DOM? jQuery?
  • it would appear that such access would need to itself be heavily sandboxed to prevent phishing attacks

Here is an example of a systemScript called helloWorld:

// A simple script tiddler that displays what it is told
// Usage:
// <<tiddler helloWorld with:Hello >>
// displays: "HelloWorld"
return $$[0] + "World";