I recently updated pocket-lint to require gjs instead of seed because the latter has been 100% broken for 6 weeks. The best thing I can say about this experience is that I am very happy there are two competing implementations of GObject Introspection bindings for JavaScript. I am disappointed that the two implementations are not 100% compatible. Most of my changes to pocket-lint were to hide the deficiencies of gjc.

There are small but important differences between gjc and seed that developers will want to be mindful of. Gjs is older, based on Spider Monkey, and servers a simple need: JavaScript is the most common development language, and GNOME should support it. Seed is newer, based on Webkit, and serves subtly different need: I know JavaScript and I want to develop GNOME applications. Gjs works though you might not know it given the lack of documentation, and you might be disappointed to see that it recommits JavaScript's original sin of namespace pollution. Seed is well documented and its extensions are in a separate namespace. Seed's documentation is 99% compatible with gjs, so I can forgive the oversight. I learned missing crucial 1% of gjs by reading the C source. I was appalled to discover that gjs creates print, log, and argv functions in the global namespace. Seed, being an implementation for developers who really use JS, place the extensions in the Seed object.

I want to use seed, but given that it is broken in Ubuntu Oneiric, I decided to support gjs. I chose to check for the existence of the Seed object, and construct one from gjs when it is not present. The namespace is still polluted. The interpreters have different command lines, though they are similar enough for my purposes.

I think the GNOME community could do better by updating the gjs and seed to share the same command line, and add extensions to a common namespace, such as System. Thus an app that wants to call System.print() will not care about which interpreter is used. This permits developer and distros to choose the backend of their choice. It also lets us change our minds.

PS. I know that some developers want to use gjs to use the JavaScript advances developed by the Mozilla community, but this is a fools pursuit. JS has been fragmented since the release of IE 3.0 in 1996. JS developers know they have to write for a common language, and use libs to provide extensions. I am very aware of the failure of ES4. I hope Mozilla can get its extensions into the official language.