为什么 CoffeeScript 将类定义包装在闭包中?

In CoffeeScript, this:

class Foo
  method: (x) ->
    x+1

编译为:

// Generated By CoffeeScript
Foo = (function() {
  function Foo() {}
  Foo.prototype.method = function(x) {
    return x+1;
  }
  return Foo;
})()

这似乎有点过分了.以下内容应功能相同:

// Generated by Dave
function Foo() {}
Foo.prototype.method = function(x) {
    return x+1;
}

Foo=function(){function e(){}return e.prototype.method=function(e){return e+1},e}();

function Foo(){}Foo.prototype.method=function(e){return e+1};