Fixing timing of onDragStart (#676)

src/state/middleware/hooks.js

@@ -239,15 +239,21 @@ export default (getHooks: () => Hooks, announce: Announce): Middleware => {
   return (store: MiddlewareStore) => (next: Dispatch) => (
     action: Action,
   ): any => {
-    // letting the reducer update first
-    next(action);
-
     if (action.type === 'INITIAL_PUBLISH') {
       const critical: Critical = action.payload.critical;
+      // Need to fire the onDragStart hook before the connected components are rendered
+      // This is so consumers can do work in their onDragStart function
+      // before we have applied any inline styles to anything,
+      // such as position: fixed to the dragging item.
+      // This is important for use cases such as a table which uses dimension locking
       publisher.start(critical);
+      next(action);
       return;
     }
 
+    // All other hooks can fire after we have updated our connected components
+    next(action);
+
     // Drag end
     if (action.type === 'DROP_COMPLETE') {
       const result: DropResult = action.payload;

stories/src/table/with-dimension-locking.jsx

@@ -233,6 +233,7 @@ export default class TableApp extends Component<AppProps, AppState> {
       }
     })();
 
+    // eslint-disable-next-line no-console
     console.log('was copied?', wasCopied);
 
     // clear selection
@@ -249,7 +250,9 @@ export default class TableApp extends Component<AppProps, AppState> {
           <Header>
             <LayoutControl>
               Current layout: <code>{this.state.layout}</code>
-              <button onClick={this.toggleTableLayout}>Toggle</button>
+              <button type="button" onClick={this.toggleTableLayout}>
+                Toggle
+              </button>
             </LayoutControl>
             <div>
               Copy table to clipboard:

test/unit/integration/hooks-timing.spec.js

@@ -0,0 +1,110 @@
+// @flow
+import React from 'react';
+import { getRect } from 'css-box-model';
+import invariant from 'tiny-invariant';
+import { mount, type ReactWrapper } from 'enzyme';
+import { DragDropContext, Draggable, Droppable } from '../../../src';
+import { getComputedSpacing } from '../../utils/dimension';
+import { withKeyboard } from '../../utils/user-input-util';
+import * as keyCodes from '../../../src/view/key-codes';
+import type { Provided as DraggableProvided } from '../../../src/view/draggable/draggable-types';
+import type { Provided as DroppableProvided } from '../../../src/view/droppable/droppable-types';
+import type { Hooks } from '../../../src/types';
+
+const pressSpacebar = withKeyboard(keyCodes.space);
+
+type ItemProps = {|
+  provided: DraggableProvided,
+  onRender: Function,
+|};
+
+class Item extends React.Component<ItemProps> {
+  render() {
+    this.props.onRender();
+    const provided: DraggableProvided = this.props.provided;
+    return (
+      <div
+        className="drag-handle"
+        ref={provided.innerRef}
+        {...provided.draggableProps}
+        {...provided.dragHandleProps}
+      >
+        <h4>Draggable</h4>
+      </div>
+    );
+  }
+}
+
+jest.useFakeTimers();
+
+it('should call the onDragStart before any connected components are updated', () => {
+  let onDragStartTime: ?DOMHighResTimeStamp = null;
+  let renderTime: ?DOMHighResTimeStamp = null;
+  const hooks: Hooks = {
+    onDragStart: jest.fn().mockImplementation(() => {
+      invariant(!onDragStartTime, 'onDragStartTime already set');
+      onDragStartTime = performance.now();
+    }),
+    onDragEnd: jest.fn(),
+  };
+  const onItemRender = jest.fn().mockImplementation(() => {
+    invariant(!renderTime, 'renderTime already set');
+    renderTime = performance.now();
+  });
+  // Both list and item will have the same dimensions
+  jest
+    .spyOn(Element.prototype, 'getBoundingClientRect')
+    .mockImplementation(() =>
+      getRect({
+        top: 0,
+        left: 0,
+        right: 100,
+        bottom: 100,
+      }),
+    );
+
+  // Stubbing out totally - not including margins in this
+  jest
+    .spyOn(window, 'getComputedStyle')
+    .mockImplementation(() => getComputedSpacing({}));
+  const wrapper: ReactWrapper = mount(
+    <DragDropContext {...hooks}>
+      <Droppable droppableId="droppable">
+        {(droppableProvided: DroppableProvided) => (
+          <div
+            ref={droppableProvided.innerRef}
+            {...droppableProvided.droppableProps}
+          >
+            <h2>Droppable</h2>
+            <Draggable draggableId="draggable" index={0}>
+              {(draggableProvided: DraggableProvided) => (
+                <Item onRender={onItemRender} provided={draggableProvided} />
+              )}
+            </Draggable>
+          </div>
+        )}
+      </Droppable>
+    </DragDropContext>,
+  );
+
+  pressSpacebar(wrapper.find('.drag-handle'));
+
+  // clearing the first call
+  expect(onItemRender).toHaveBeenCalledTimes(1);
+  renderTime = null;
+  onItemRender.mockClear();
+
+  // run out prepare phase
+  jest.runOnlyPendingTimers();
+
+  // checking values are set
+  invariant(onDragStartTime, 'onDragStartTime should be set');
+  invariant(renderTime, 'renderTime should be set');
+
+  // core assertion
+  expect(onDragStartTime).toBeLessThan(renderTime);
+
+  // validation
+  expect(hooks.onDragStart).toHaveBeenCalledTimes(1);
+  expect(onItemRender).toHaveBeenCalledTimes(1);
+});