顶级变量不是全局范围的，在 CoffeeScript 中返回值是强制性的

funName = () ->
  $(".foo").addClass("bar");

Compiles into the scope of an anonymous function. Calling funName from the console results in undefined.

(function() {
  var funName;
  funName = function() {
    return $(".foo").addClass("bar");
  };
}).call(this);

What's its reasoning for compiling like this and how do I work with it?

Also any insight on the mandatory return within functions using CoffeeScript would be great. Why is it like that? How do I need to code differently because of it?

解决方案

Mike has answered the main question here. The modular wrapper a common point of confusion for CoffeeScript newcomers, as illustrated by these related questions:

• How do I define global variables in CoffeeScript?
• Why use the javascript function wrapper (added in coffeescript) ".call(this)"
• Getting rid of CoffeeScript's closure wrapper

As to your other question: If you don't want a function to return anything, simply make the last line of that function either return by itself or, equivalently, undefined. Either will compile to a function with no return. For instance:

funName = ->
  $(".foo").addClass "bar"
  return

compiles to

var funName;
funName = function() {
  $(".foo").addClass("bar");
};

Note that there is an ongoing discussion (issue 899) about a possible alternative syntax for defining no-return functions. If the current proposal were accepted, you'd be able to write your function as

funName = -/> $(".foo").addClass "bar"

If you like that syntax, you should voice your support for it.