docs/anatomy/tasks/config/coffee.js.md
This file configures a Grunt task called "coffee".
By default, this compiles CoffeeScript files located in assets/js/ into JavaScript, then generates new .js files in .tmp/public/js/.
No problem!
If you aren't using any kind of pre-processing for your client-side JavaScript, then just ignore this file.
If you want to use a different pre-processor like TypeScript or Babel, and you want Sails to process your client-side JavaScript assets automatically as you work, then you're in luck. In most cases, this is as easy as installing the appropriate Grunt plugin as a dependency of your Sails app, and then configuring it to output compiled JavaScript to the same path as in this default task.
Here are a couple of popular examples:
For additional usage documentation, see grunt-contrib-coffee.