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Dropbox drops JavaScript, brews CoffeeScript

23,000 lines of code converted, but why?

Dropbox has stopped using JavaScript whenever it codes for browsers and has instead adopted CoffeeScript by re-writing 23,000 lines of code.

DropBox developers Dan W, Ziga M and Chris V explain their choice in a blog post, offering brevity of syntax as their main concern and citing the following statistics from the company's re-coding project as evidence of CoffeeScript's lesser burden for developers.

JavaScript CoffeeScript
Lines of code 23437 18417
Tokens 75334 66058
Characters 865613 659930

That 5000 fewer lines of code, the developers write, “is beneficial for simple reasons — being able to fit more code into a single editor screen, for example.”

“Measuring reduction in code complexity is of course much harder,” the coders add, “but we think the stats above, especially token count, are a good first-order approximation.”

Astute Reg readers may, at this point, wonder why it makes sense to bother replacing 23,000 lines of code when CoffeeScript compiles down into JavaScript anyway.

Indeed, while the developers feel more productive, there's no indication the site works better after the transition to the new scripting language. “The size of the compressed bundle didn’t change significantly pre- and post-coffee transformation, so our users shouldn’t notice anything different,” the trio write. “The site performs and behaves as before.”

The developers are Python-lovers, and that language is a source of inspiration for CoffeeScript's creators. The move to CoffeeScript therefore offered the chance to code in a more Python-like environment, something that's tough to do given JavaScript's slow evolution. The fact that the re-coding process took place during a week-long hackathon is another clue to the project's motivation.

There's nothing new, of course, about software re-platforming projects. Here in El Reg's antipodean eyrie we've covered (in past lives) a few aimed at extending the life of applications written in legacy languages. Those projects, however, had a commercial outcome as their rationale. It's unclear if that's the case here. ®

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