CoffeeScript code compiles one-to-one into the equivalent JavaScript, and there is no interpretation at runtime. You can use any existing JavaScript library seamlessly from CoffeeScript (and vice-versa). The compiled output is readable and pretty-printed, passes through JavaScript Lint without warnings, will work in every JavaScript implementation, and tends to run as fast or faster than the equivalent handwritten JavaScript.
Nice basic tutorial is available at
http://adamjspooner.github.com/coffeescript-meet-backbonejs/[
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