So after getting spun into another infinite error loop while editing a JavaScript file, I discovered that the error dialog is thankfully modeless. I was able to save the file and close it to stop the infinite error loop.
Powertip: You can right click on files and use the "Open With" submenu to select the plain old text editor for JavaScript files.
This means you lose syntax highlighting. But you also lose the chance for the editor to die and the useless syntax checking. Yes, I'm sure that node really does have a "setAttribute" function, even without a class-cast. (Or whatever you'd need to do to convince the syntax checker to shut up.)
On the downside, Eclipse now supports spellchecking, and flags basically everything as misspelled. (At least as 3.4 it allows you to view suggestions, where as before it just complained.)