Objective-J's code importer is one of the more complex pieces (as it manages to do so completely asynchronously). All the approaches that use a simple JavaScript function to grab code, like grab_and_eval("file.js") are forced to happen synchronously (since you have to guarantee that the code is evaled before the next line). Without some sort of lexing support, its really not possible to both grab files asynchronously and also be able to continue executing.

Also, as stated in the article, you can't intercept JavaScript method calls, so if you want something like method missing you're forced to do something like:

call_method_or_send_method_missing(object, "method_name")

And again, since Objective-J is a proper superset of JavaScript, it doesn't lose any of its powerful features.

"There is also the issue that implementing things like method_missing and import are prohibitively difficult without new syntax."

I don't understand how you can say that, when the entire article is a defense of why they added a bunch of features to Javascript as a library. That is, as opposed to adding those features as part of a new language specification.

I think the actual argument is "as long as you are adding language features as a library, you might as well introduce new syntax for them while you're at it." They present several arguments in defense of this claim.

But, with Objective-J you can write for example, some math library that has nothing to do with Cappuccino and not load Cappuccino.