Add comment function

src/Native/VirtualDom.js

@@ -22,6 +22,14 @@ function text(string)
 	};
 }
 
+function comment(string)
+{
+	return {
+		type: 'comment',
+		text: string
+	};
+}
+
 
 function node(tag)
 {
@@ -320,6 +328,9 @@ function render(vNode, eventNode)
 		case 'text':
 			return localDoc.createTextNode(vNode.text);
 
+		case 'comment':
+			return localDoc.createComment(vNode.text);
+
 		case 'node':
 			var domNode = vNode.namespace
 				? localDoc.createElementNS(vNode.namespace, vNode.tag)
@@ -649,6 +660,15 @@ function diffHelp(a, b, patches, index)
 
 			return;
 
+		case 'comment':
+			if (a.text !== b.text)
+			{
+				patches.push(makePatch('p-comment', index, b.text));
+				return;
+			}
+
+			return;
+
 		case 'node':
 			// Bail if obvious indicators have changed. Implies more serious
 			// structural changes such that it's not worth it to diff.
@@ -1205,8 +1225,9 @@ function addDomNodesHelp(domNode, vNode, patches, i, low, high, eventNode)
 			return i;
 
 		case 'text':
+		case 'comment':
 		case 'thunk':
-			throw new Error('should never traverse `text` or `thunk` nodes like this');
+			throw new Error('should never traverse `text`, `comment` or `thunk` nodes like this');
 	}
 }
 
@@ -1256,6 +1277,10 @@ function applyPatch(domNode, patch)
 			domNode.replaceData(0, domNode.length, patch.data);
 			return domNode;
 
+		case 'p-comment':
+			domNode.replaceData(0, domNode.length, patch.data);
+			return domNode;
+
 		case 'p-thunk':
 			return applyPatchesHelp(domNode, patch.data);
 
@@ -1858,6 +1883,7 @@ var allEvents = mostEvents.concat('wheel', 'scroll');
 return {
 	node: node,
 	text: text,
+	comment: comment,
 	custom: custom,
 	map: F2(map),
 

src/VirtualDom.elm

@@ -1,6 +1,6 @@
 module VirtualDom exposing
   ( Node
-  , text, node
+  , text, node, comment
   , Property, property, attribute, attributeNS, mapProperty
   , style
   , on, onWithOptions, Options, defaultOptions
@@ -14,7 +14,7 @@ module VirtualDom exposing
 that expose more helper functions for HTML or SVG.
 
 # Create
-@docs Node, text, node
+@docs Node, text, node, comment
 
 # Declare Properties and Attributes
 @docs Property, property, attribute, attributeNS, mapProperty
@@ -77,6 +77,16 @@ text =
   Native.VirtualDom.text
 
 
+{-| Create a comment node in the DOM. It will escape the string just like it
+does for `text`.
+
+    comment "This is a comment"
+-}
+comment : String -> Node msg
+comment =
+    Native.VirtualDom.comment
+
+
 {-| This function is useful when nesting components with [the Elm
 Architecture](https://github.com/evancz/elm-architecture-tutorial/). It lets
 you transform the messages produced by a subtree.
@@ -328,4 +338,3 @@ programWithFlags
   -> Program flags model msg
 programWithFlags impl =
   Native.VirtualDom.programWithFlags Debug.wrapWithFlags impl
-