Sequential modx/goto_position hits correct multicourse URL

common/lib/xmodule/xmodule/js/src/sequence/display.coffee

@@ -3,6 +3,8 @@ class @Sequence
     @el = $(element).find('.sequence')
     @contents = @$('.seq_contents')
     @id = @el.data('id')
+    @modx_url = @$('#course_modx_root').text()
+    @modx_url = @modx_url.substr(1,@modx_url.length-2) # Remove enclosing quotes
     @initProgress()
     @bind()
     @render parseInt(@el.data('position'))
@@ -76,7 +78,8 @@ class @Sequence
     if @position != new_position
       if @position != undefined
         @mark_visited @position
-        $.postWithPrefix "/modx/#{@id}/goto_position", position: new_position
+        modx_full_url = @modx_url + '/' + @id + '/goto_position'
+        $.postWithPrefix modx_full_url, position: new_position
 
       @mark_active new_position
       @$('#seq_content').html @contents.eq(new_position - 1).text()
@@ -91,7 +94,7 @@ class @Sequence
     event.preventDefault()
     new_position = $(event.target).data('element')
     Logger.log "seq_goto", old: @position, new: new_position, id: @id
-
+    
     # On Sequence chage, destroy any existing polling thread 
     #   for queued submissions, see ../capa/display.coffee
     if window.queuePollerID

lms/templates/seq_module.html

 <div id="sequence_${element_id}" class="sequence" data-id="${item_id}" data-position="${position}" >
+  <span style="display:none" id="course_modx_root">"/course/modx"</span>
   <nav aria-label="Section Navigation" class="sequence-nav">
     <ol id="sequence-list">
       % for idx, item in enumerate(items):