CoffeeScript has one single rule : "It's just JavaScript." The main idea behind CoffeeScript is to create a langage that is easily readable. CoffeeScript is transpiled in JavaScript, meaning that it has to be converted into regular JavaScript before being used. Its syntax is very close to Ruby. For example, parenthesis are optional (as long as the syntax is not misinterpreted), the last result is automatically returned (no need for any return statement), the "if" statement can be placed at the end of the expression, and much more. CoffeeScript is an interesting language for those who like to have clear, readable and light code. As it's basically JavaScript, it does not damage the performance aspect, and is a different way to approach a JavaScript project.