optimizations: setState in lifecycles + forced reflow (#556)

Author: avoskresensky

lib/Draggable.js

@@ -236,7 +236,9 @@ class Draggable extends React.Component<DraggableProps, DraggableState> {
   }
 
   componentWillUnmount() {
-    this.setState({dragging: false}); // prevents invariant if unmounted while dragging
+    if (this.state.dragging) {
+      this.setState({dragging: false}); // prevents invariant if unmounted while dragging
+    }
   }
 
   // React Strict Mode compatibility: if `nodeRef` is passed, we will use it instead of trying to find

lib/DraggableCore.js

@@ -265,7 +265,16 @@ export default class DraggableCore extends React.Component<DraggableCoreProps> {
       removeEvent(ownerDocument, eventsFor.mouse.stop, this.handleDragStop);
       removeEvent(ownerDocument, eventsFor.touch.stop, this.handleDragStop);
       removeEvent(thisNode, eventsFor.touch.start, this.onTouchStart, {passive: false});
-      if (this.props.enableUserSelectHack) removeUserSelectStyles(ownerDocument);
+      if (this.props.enableUserSelectHack) {
+        // prevent a possible "forced reflow"
+        if (window.requestAnimationFrame) {
+          window.requestAnimationFrame(() => {
+            removeUserSelectStyles(ownerDocument);
+          });
+        } else {
+          removeUserSelectStyles(ownerDocument);
+        }
+      }
     }
   }