Add markdown preview; fix bug with deleted editor

app/assets/javascripts/editor.js

@@ -0,0 +1,55 @@
+$(function() {
+
+  $('.md_editor .field_container .preview-button').click(function() {
+    if ($(this).data('preview') == 'true') {
+      edit($(this));
+    } else {
+      preview($(this));
+    }
+  });
+
+  function edit(target) {
+    target.data('preview', 'false');
+    target.text('Preview');
+    target.parent().find('.preview').hide();
+    target.parent().find('.editor_field').show();
+  }
+
+  function preview(target) {
+    target.data('preview', 'true');
+    target.text('Edit');
+    var prev   = target.parent().find('.preview');
+    var editor = target.parent().find('.editor_field')
+    prev.html("<i>(Loading ...)</i>");
+    prev.show();
+    editor.hide()
+    if (target.parent().parent().hasClass('mini')) {
+      var url = '/tools/render_mini_markdown';
+    } else {
+      var url = '/tools/render_markdown';
+    }
+    $.ajax(url, {
+      type: 'post',
+      data: {text: editor.val()},
+      dataType: 'html',
+      headers: {
+        'X-CSRF-Token': $('meta[name="csrf-token"]').attr('content')
+      },
+      success: function(data) {
+        prev.html(data);
+        prev.find('pre code').each(function(i, e) {
+          if ($(this).attr("class")) {
+            $(this).parent().attr("lang", $(this).attr("class").replace("hljs", "").trim());
+          } else {
+            $(this).parent().attr("lang", "(language unknown)");
+          }
+          hljs.highlightBlock(e);
+        });
+      },
+      error: function(xhr, status, err) {
+        prev.html('<i>(Error: ' + status + ')</i><br>' + err);
+      }
+    });
+  }
+
+});