clear response pane after posting

lms/static/coffee/src/discussion/views/discussion_content_view.coffee

@@ -71,6 +71,18 @@ class @DiscussionContentView extends Backbone.View
       @$local = @$el
     @$delegateElement = @$local
 
+  makeWmdEditor: (cls_identifier) =>
+    DiscussionUtil.makeWmdEditor @$el, $.proxy(@$, @), cls_identifier
+
+  getWmdEditor: (cls_identifier) =>
+    DiscussionUtil.getWmdEditor @$el, $.proxy(@$, @), cls_identifier
+
+  getWmdContent: (cls_identifier) =>
+    DiscussionUtil.getWmdContent @$el, $.proxy(@$, @), cls_identifier
+
+  setWmdContent: (cls_identifier, text) =>
+    DiscussionUtil.setWmdContent @$el, $.proxy(@$, @), cls_identifier, text
+
   initialize: ->
     @initLocal()
     @model.bind('change', @renderPartialAttrs, @)

lms/static/coffee/src/discussion/views/discussion_thread_view.coffee

@@ -26,7 +26,7 @@ class @DiscussionThreadView extends DiscussionContentView
     @renderVoted()
     @renderAttrs()
     @$("span.timeago").timeago()
-    Markdown.makeWmdEditor @$(".reply-body"), "", DiscussionUtil.urlFor("upload"), (text) -> DiscussionUtil.postMathJaxProcessor(text)
+    @makeWmdEditor "reply-body"
     @convertMath()
     @renderResponses()
     @highlight @$(".post-body")
@@ -50,7 +50,7 @@ class @DiscussionThreadView extends DiscussionContentView
   convertMath: ->
     element = @$(".post-body")
     element.html DiscussionUtil.postMathJaxProcessor(element.html())
-    MathJax.Hub.Queue ["Typeset", MathJax.Hub, element.attr("id")]
+    MathJax.Hub.Queue ["Typeset", MathJax.Hub, element[0]]
 
   renderResponses: ->
     DiscussionUtil.safeAjax
@@ -119,7 +119,9 @@ class @DiscussionThreadView extends DiscussionContentView
   submitComment: (event) ->
     event.preventDefault()
     url = @model.urlFor('reply')
-    body = @$("#wmd-input").val()
+    body = @getWmdContent("reply-body")
+    return if not body.trim().length
+    @setWmdContent("reply-body", "")
     response = new Comment(body: body, created_at: (new Date()).toISOString(), username: window.user.get("username"), votes: { up_count: 0 }, endorsed: false, user_id: window.user.get("id"))
     response.set('thread', @model.get('thread'))
     @renderResponse(response)

lms/static/sass/_discussion.scss

@@ -1426,15 +1426,15 @@ body.discussion {
     }
   }
 
-  #wmd-button-bar {
+  .wmd-button-bar {
     border: none;
   }
 
-  #wmd-input {
+  .wmd-input {
     @include discussion-wmd-input;
   }
 
-  #wmd-preview {
+  .wmd-preview {
     @include discussion-wmd-preview;
   }