update rotation of transformer automatically. close #976

src/Node.ts

@@ -665,7 +665,7 @@ export abstract class Node<Config extends NodeConfig = NodeConfig> {
    * @method
    * @name Konva.Node#on
    * @param {String} evtStr e.g. 'click', 'mousedown touchstart', 'mousedown.foo touchstart.foo'
-   * @param {Function} handler The handler function is passed an event object
+   * @param {Function} handler The handler function. The first argument of that function is event object. Event object has `target` as main target of the event, `currentTarget` as current node listener and `evt` as native browser event.
    * @returns {Konva.Node}
    * @example
    * // add click listener

src/shapes/Transformer.ts

@@ -292,6 +292,11 @@ export class Transformer extends Group {
         .join(' ');
 
       const onChange = () => {
+        //
+        if (this.nodes().length === 1) {
+          this.rotation(this.nodes()[0].rotation());
+        }
+
         this._resetTransformCache();
         if (!this._transforming) {
           this.update();