Function declaration in CoffeeScript

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CoffeeScript uses function declarations (aka “named functions”) in just one place: class definitions. For instance,

class Foo

compiles to

var Foo;
Foo = (function() {
  function Foo() {}
  return Foo;
})();

The reason CoffeeScript doesn’t use function declarations elsewhere, according to the FAQ:

Blame Microsoft for this one. Originally every function that could have a sensible name retrieved for it was given one, but IE versions 8 and down have scoping issues where the named function is treated as both a declaration and an expression. See this for more information.

In short: Using function declarations carelessly can lead to inconsistencies between IE (pre-9) and other JS environments, so CoffeeScript eschews them.

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