Getters and setters are a Javascript 1.6 (IIRC) language feature that lets you provide interfaces that look and feel like DOM 0 interfaces, where you read and set a variable or property like document.title or document.links, and receive something that may or may not require computation, compositing and much else behind the scenes. The only news is that you can now implement things like the location object (set href and affect all the other properties in one go) from mere javascript and that the syntax is even rather friendly, by javascript standards:
var myLoc = (function() {
var url; // private variable hidden in the function closure
return {
toString: function() {
return this.href;
},
get href() {
return url;
},
set href(h) {
return url = h;
},
get prototcol() {
return url.match(/^.*?:/)[0];
},
set protocol(p) {
url = p + url.match(/^.*:(.*)/)[1];
return p;
}
};
})();alert(myLoc), and so on. It's a dream for making APIs that don't feel like java pushed down your throat with a ten-foot pole.I've been meaning to add some features to Greasemonkey to grant it proper introspection (as all great software systems are introspective), for the Greasemonkey header block, and once I thought twice about it, for the source code at large. Something like a
self object, with a "source" property for the code and a headers property for the parsed headers -- so self.headers.include would be the array of all @include headers, and so on.I wanted that feature to give anybody the option to make their own cool extensions and libraries to Greasemonkey, making use of structured information -- much like an @xpath feature I've been noodling on on and off over the past few months to make GM scripts much more maintainable (and quick to write, and, optionally, self deprecating).
Anyway, the natural way of implementing this is via getters, and I was just about done when I hit a wall with Mozilla's extension API which wouldn't let the script executing in the Greasemonkey sandbox read my exposed getter variable (at the time named GM_headers): it threw a "Permission denied to get property Sandbox.GM_headers" exception when code accessed GM_headers, and that was that. Is this feature crippled for extensions wanting to provide getter / setter APIs from javascript code, or do I miss some incantations to bless the sandboxed code to read that?
The (hopefully) full picture of relevant details, surrounding my implementation:
var safeWin = new XPCNativeWrapper(unsafeContentWin);
var sandbox = new Components.utils.Sandbox(safeWin);
// ...
sandbox.__proto__ = {
get GM_headers() {
return headers.get();
}
};
sandbox.__proto__.__proto__ = safeWin;