Is there a sass tool for Javascript?

Is there a tool like Sass for Javascript? To be more specific:

A tool that allows the user to include multiple javascript files via a special syntax and watch for any changes on the files included. Once a change occurs on one or more of those开发者_如何学编程 files, the tool should concatenate and compress the files and ideally do some error checking along the way. The results should be included in a single file.

I'm looking for a tool that runs in the background while I'm coding, not a server or client side tool like minify or less.js

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You can try CoffeeScript but you need to compile oyur .coffee to make a .js