gistfile1.js

var map = function (fn) { return function (arr) { return jQuery.map(arr, fn); } };
var each = function (fn) { return function (arr) { jQuery.each(arr, fn); } };

loadReplies: function() {
  var _this = this, request;

  request = jQuery.getJSON('/posts/' + this.get('id') + '/replies')
    .then(map(Discourse.Post.create))
    .then(each(function (post) { post.set('topic', _this.get('topic'); }))

  this.set('replies', []);
  request.done(function (replies) { _this.set('replies', replies); });

  this.set('loadingReplies', true);
  request.done(function () { _this.set('loadingReplies', false); });

  return request;
}

gistfile2.coffee

map = (fn) -> (arr) -> jQuery.map(arr, fn)
each = (fn) -> (arr) -> jQuery.each(arr, fn)

loadReplies: =>
  request = jQuery.getJSON("/posts/#{@get('id')}/replies")
    .then(map(Discourse.Post.create))
    .then(each((post) => post.set('topic', @get('topic'))))

  @set('replies', [])
  request.done (replies) => @set('replies', replies)

  @set('loadingReplies', true)
  request.done => @set('loadingReplies', false)

  return request