javascript – 为什么coffeescript会生成这样的类？

class Animal
  constructor: (@Name) ->
  speak: (things) -> "My name is #{@namE} and I like #{things}"

这是生成的：

var Animal = (function() {
  function Animal(Name) {
    this.name = name;
  }
  Animal.prototype.speak = function(things) {
    return "My name is " + this.name + " and I like " + things;
  };
  return Animal;
})();

但为什么这个惯用代码不会产生呢？

var Animal = function Animal(Name) {
  this.name = name;
};
Animal.prototype.speak = function(things) {
  return "My name is " + this.name + " and I like " + things;
};

我知道coffeescript在匿名函数中包含很多东西来控制范围泄漏,但是这里可能会泄漏什么？