fix: use stored size in onResizeStop to prevent stale data

__tests__/Resizable.test.js

@@ -404,6 +404,107 @@ describe('render Resizable', () => {
         });
       });
     });
+
+    describe('onResizeStop with stale props', () => {
+      // This tests the fix for a bug where onResizeStop would report stale size data
+      // because React's batched state updates mean props.width/height haven't updated yet
+      // when onResizeStop fires. The fix stores the last size from onResize and uses it
+      // in onResizeStop. See: https://github.com/react-grid-layout/react-grid-layout/pull/2224
+
+      test('onResizeStop reports correct size even when props are stale', () => {
+        const onResizeStop = jest.fn();
+        const onResize = jest.fn();
+        const resizableRef = React.createRef();
+        render(
+          <Resizable {...customProps} onResize={onResize} onResizeStop={onResizeStop} ref={resizableRef}>
+            {resizableBoxChildren}
+          </Resizable>
+        );
+
+        // Simulate onResizeStart
+        const startHandler = resizableRef.current.resizeHandler('onResizeStart', 'se');
+        startHandler(mockEvent, { node, deltaX: 0, deltaY: 0 });
+
+        // Simulate dragging - this calls onResize with the new size
+        const dragHandler = resizableRef.current.resizeHandler('onResize', 'se');
+        dragHandler(mockEvent, { node, deltaX: 20, deltaY: 30 });
+        expect(onResize).toHaveBeenLastCalledWith(
+          mockEvent,
+          expect.objectContaining({
+            size: { width: 70, height: 80 },
+          })
+        );
+
+        // Now simulate onResizeStop. In a real app, React may not have re-rendered yet,
+        // so props.width/height would still be 50. The deltaX/deltaY from DraggableCore's
+        // onStop is typically 0 or very small since the mouse hasn't moved since the last
+        // drag event. Without the fix, this would incorrectly report size: {width: 50, height: 50}.
+        const stopHandler = resizableRef.current.resizeHandler('onResizeStop', 'se');
+        stopHandler(mockEvent, { node, deltaX: 0, deltaY: 0 });
+
+        // With the fix, onResizeStop should report the same size as the last onResize
+        expect(onResizeStop).toHaveBeenCalledWith(
+          mockEvent,
+          expect.objectContaining({
+            size: { width: 70, height: 80 },
+          })
+        );
+      });
+
+      test('onResizeStop reports correct size for west handle with stale props', () => {
+        const onResizeStop = jest.fn();
+        const onResize = jest.fn();
+        const resizableRef = React.createRef();
+        const testMockClientRect = { left: 0, top: 0 };
+        const testNode = document.createElement('div');
+        testNode.getBoundingClientRect = () => ({ ...testMockClientRect });
+
+        render(
+          <Resizable {...customProps} onResize={onResize} onResizeStop={onResizeStop} ref={resizableRef}>
+            {resizableBoxChildren}
+          </Resizable>
+        );
+
+        // Simulate onResizeStart - this sets lastHandleRect to {left: 0, top: 0}
+        const startHandler = resizableRef.current.resizeHandler('onResizeStart', 'w');
+        startHandler(mockEvent, { node: testNode, deltaX: 0, deltaY: 0 });
+
+        // Simulate dragging west (left)
+        // deltaX = -15 from drag, plus position adjustment of -15 (handle moved from 0 to -15)
+        // Total deltaX = -30, reversed for 'w' = +30, so width = 50 + 30 = 80
+        const dragHandler = resizableRef.current.resizeHandler('onResize', 'w');
+        testMockClientRect.left = -15;
+        dragHandler(mockEvent, { node: testNode, deltaX: -15, deltaY: 0 });
+        expect(onResize).toHaveBeenLastCalledWith(
+          mockEvent,
+          expect.objectContaining({
+            size: { width: 80, height: 50 },
+          })
+        );
+
+        // Continue dragging - element moves further left
+        // position adjustment: -25 - (-15) = -10, deltaX becomes -10 + (-10) = -20
+        // reversed for 'w' = +20, width = 50 + 20 = 70
+        testMockClientRect.left = -25;
+        dragHandler(mockEvent, { node: testNode, deltaX: -10, deltaY: 0 });
+        expect(onResize).toHaveBeenLastCalledWith(
+          mockEvent,
+          expect.objectContaining({
+            size: { width: 70, height: 50 },
+          })
+        );
+
+        // onResizeStop with stale props - should use stored lastSize (70x50 from last onResize)
+        const stopHandler = resizableRef.current.resizeHandler('onResizeStop', 'w');
+        stopHandler(mockEvent, { node: testNode, deltaX: 0, deltaY: 0 });
+        expect(onResizeStop).toHaveBeenCalledWith(
+          mockEvent,
+          expect.objectContaining({
+            size: { width: 70, height: 50 },
+          })
+        );
+      });
+    });
   });
 
   // ============================================
@@ -588,14 +689,17 @@ describe('render Resizable', () => {
       const node = document.createElement('div');
       node.getBoundingClientRect = () => ({ left: 0, top: 0 });
 
-      // First start
+      // Start resize
       const startHandler = resizableRef.current.resizeHandler('onResizeStart', 'se');
       startHandler(mockEvent, { node, deltaX: 0, deltaY: 0 });
 
-      // Then stop with a delta - Resizable is stateless so size is calculated from
-      // props.width/height + delta at time of stop
+      // Drag to resize - this stores the size for onResizeStop to use
+      const dragHandler = resizableRef.current.resizeHandler('onResize', 'se');
+      dragHandler(mockEvent, { node, deltaX: 10, deltaY: 10 });
+
+      // Stop resize - uses the stored size from the last onResize
       const stopHandler = resizableRef.current.resizeHandler('onResizeStop', 'se');
-      stopHandler(mockEvent, { node, deltaX: 10, deltaY: 10 });
+      stopHandler(mockEvent, { node, deltaX: 0, deltaY: 0 });
 
       expect(props.onResizeStop).toHaveBeenCalledWith(
         mockEvent,

lib/Resizable.js

@@ -24,13 +24,14 @@ export default class Resizable extends React.Component<Props, void> {
   handleRefs: {[key: ResizeHandleAxis]: ReactRef<HTMLElement>} = {};
   lastHandleRect: ?ClientRect = null;
   slack: ?[number, number] = null;
+  lastSize: ?{width: number, height: number} = null;
 
   componentWillUnmount() {
     this.resetData();
   }
 
   resetData() {
-    this.lastHandleRect = this.slack = null;
+    this.lastHandleRect = this.slack = this.lastSize = null;
   }
 
   // Clamp width and height within provided constraints
@@ -132,8 +133,20 @@ export default class Resizable extends React.Component<Props, void> {
       // Run user-provided constraints.
       [width, height] = this.runConstraints(width, height);
 
+      // For onResizeStop, use the last size from onResize rather than recalculating.
+      // This avoids issues where props.width/height are stale due to React's batched updates.
+      if (handlerName === 'onResizeStop' && this.lastSize) {
+        ({width, height} = this.lastSize);
+      }
+
       const dimensionsChanged = width !== this.props.width || height !== this.props.height;
 
+      // Store the size for use in onResizeStop. We do this after the onResizeStop check
+      // above so we don't overwrite the stored value with a potentially stale calculation.
+      if (handlerName !== 'onResizeStop') {
+        this.lastSize = {width, height};
+      }
+
       // Call user-supplied callback if present.
       const cb = typeof this.props[handlerName] === 'function' ? this.props[handlerName] : null;
       // Don't call 'onResize' if dimensions haven't changed.