Add on beforeElAttrsUpdated callback

README.md

@@ -89,7 +89,8 @@ Supported options (all optional):
 - **addChild** (`Function(parentNode, childNode)`) - Called when adding a new child to a parent. By default, `parentNode.appendChild(childNode)` is invoked. Use this callback to customize how a new child is added.
 - **onBeforeNodeAdded** (`Function(node)`) - Called before a `Node` in the `to` tree is added to the `from` tree. If this function returns `false` then the node will not be added. Should return the node to be added.
 - **onNodeAdded** (`Function(node)`) - Called after a `Node` in the `to` tree has been added to the `from` tree.
-- **onBeforeElUpdated** (`Function(fromEl, toEl)`) - Called before a `HTMLElement` in the `from` tree is updated. If this function returns `false` then the element will not be updated.
+- **onBeforeElUpdated** (`Function(fromEl, toEl)`) - Called before a `HTMLElement` in the `from` tree is updated. If this function returns `false` then the element will not be updated. Also its children won't be processed.
+- **onBeforeElAttrsUpdated** (`Function(fromEl, toEl)`) - Called before a `HTMLElement` in the `from` tree is updated. If this function returns `false` then the element will not be updated. Its children will still be processed.
 - **onElUpdated** (`Function(el)`) - Called after a `HTMLElement` in the `from` tree has been updated.
 - **onBeforeNodeDiscarded** (`Function(node)`) - Called before a `Node` in the `from` tree is discarded. If this function returns `false` then the node will not be discarded.
 - **onNodeDiscarded** (`Function(node)`) - Called after a `Node` in the `from` tree has been discarded.

src/morphdom.js

@@ -39,6 +39,7 @@ export default function morphdomFactory(morphAttrs) {
     var onBeforeNodeAdded = options.onBeforeNodeAdded || noop;
     var onNodeAdded = options.onNodeAdded || noop;
     var onBeforeElUpdated = options.onBeforeElUpdated || noop;
+    var onBeforeElAttrsUpdated = options.onBeforeElAttrsUpdated || noop;
     var onElUpdated = options.onElUpdated || noop;
     var onBeforeNodeDiscarded = options.onBeforeNodeDiscarded || noop;
     var onNodeDiscarded = options.onNodeDiscarded || noop;
@@ -211,8 +212,11 @@ export default function morphdomFactory(morphAttrs) {
           return;
         }
 
-        // update attributes on original DOM element first
-        morphAttrs(fromEl, toEl);
+        if (onBeforeElAttrsUpdated(fromEl, toEl) !== false) {
+          // update attributes on original DOM element first
+          morphAttrs(fromEl, toEl);
+        }
+
         // optional
         onElUpdated(fromEl);