input.coffee

class foo
  constructor: ()->
    alert 'fooBar'
  a: ->
  b: ->
  c: ->
  d: ->
  e: ->
  f: ->

output.js

var foo;
foo = function() {
  alert('fooBar');
  return this;
};
foo.prototype.a = function() {};
foo.prototype.b = function() {};
foo.prototype.c = function() {};
foo.prototype.d = function() {};
foo.prototype.e = function() {};
foo.prototype.f = function() {};

shouldOutput.js

var foo;
foo = function() {
  alert('fooBar');
  return this;
};
foo.prototype = {
  a: function() {},
  b: function() {},
  c: function() {},
  d: function() {},
  e: function() {},
  f: function() {}
};