Prevent toggling between min and max scroll offsets at end of grid

src/FixedSizeGrid.js

@@ -65,6 +65,8 @@ const FixedSizeGrid = createGridComponent({
       default:
         if (scrollLeft >= minOffset && scrollLeft <= maxOffset) {
           return scrollLeft;
+        } else if (minOffset > maxOffset) {
+          return minOffset;
         } else if (scrollLeft - minOffset < maxOffset - scrollLeft) {
           return minOffset;
         } else {
@@ -115,6 +117,8 @@ const FixedSizeGrid = createGridComponent({
       default:
         if (scrollTop >= minOffset && scrollTop <= maxOffset) {
           return scrollTop;
+        } else if (minOffset > maxOffset) {
+          return minOffset;
         } else if (scrollTop - minOffset < maxOffset - scrollTop) {
           return minOffset;
         } else {

src/VariableSizeGrid.js

@@ -274,6 +274,8 @@ const getOffsetForIndexAndAlignment = (
     default:
       if (scrollOffset >= minOffset && scrollOffset <= maxOffset) {
         return scrollOffset;
+      } else if (minOffset > maxOffset) {
+        return minOffset;
       } else if (scrollOffset - minOffset < maxOffset - scrollOffset) {
         return minOffset;
       } else {

src/__tests__/FixedSizeGrid.js

@@ -569,6 +569,81 @@ describe('FixedSizeGrid', () => {
       expect(onItemsRendered.mock.calls).toMatchSnapshot();
     });
 
+    it('should scroll to the correct item for align = "auto" at the bottom of the grid', () => {
+      getScrollbarSize.mockImplementation(() => 20);
+
+      const rendered = ReactTestRenderer.create(
+        <FixedSizeGrid {...defaultProps} rowCount={20} rowHeight={30} />
+      );
+      onItemsRendered.mockClear();
+
+      // Scroll down to the last row in the list.
+      rendered
+        .getInstance()
+        .scrollToItem({ columnIndex: 5, rowIndex: 19, align: 'auto' });
+
+      expect(onItemsRendered).toHaveBeenCalledTimes(1);
+      expect(onItemsRendered).toHaveBeenLastCalledWith(
+        expect.objectContaining({
+          visibleRowStartIndex: 17,
+          visibleRowStopIndex: 19,
+        })
+      );
+      // Repeat the previous scrollToItem call.
+      rendered
+        .getInstance()
+        .scrollToItem({ columnIndex: 5, rowIndex: 19, align: 'auto' });
+
+      // Shouldn't have been called again
+      expect(onItemsRendered).toHaveBeenCalledTimes(1);
+      expect(onItemsRendered).toHaveBeenLastCalledWith(
+        expect.objectContaining({
+          visibleRowStartIndex: 17,
+          visibleRowStopIndex: 19,
+        })
+      );
+    });
+
+    it('should scroll to the correct item for align = "auto" at the end of the grid', () => {
+      getScrollbarSize.mockImplementation(() => 20);
+
+      const rendered = ReactTestRenderer.create(
+        <FixedSizeGrid
+          {...defaultProps}
+          columnCount={20}
+          columnWidth={50}
+          width={120}
+        />
+      );
+      onItemsRendered.mockClear();
+
+      // Scroll across to the last row in the list.
+      rendered
+        .getInstance()
+        .scrollToItem({ columnIndex: 19, rowIndex: 19, align: 'auto' });
+
+      expect(onItemsRendered).toHaveBeenCalledTimes(1);
+      expect(onItemsRendered).toHaveBeenLastCalledWith(
+        expect.objectContaining({
+          visibleColumnStartIndex: 18,
+          visibleColumnStopIndex: 19,
+        })
+      );
+      // Repeat the previous scrollToItem call.
+      rendered
+        .getInstance()
+        .scrollToItem({ columnIndex: 19, rowIndex: 19, align: 'auto' });
+
+      // Shouldn't have been called again
+      expect(onItemsRendered).toHaveBeenCalledTimes(1);
+      expect(onItemsRendered).toHaveBeenLastCalledWith(
+        expect.objectContaining({
+          visibleColumnStartIndex: 18,
+          visibleColumnStopIndex: 19,
+        })
+      );
+    });
+
     it('should scroll to the correct item for align = "start"', () => {
       const rendered = ReactTestRenderer.create(
         <FixedSizeGrid {...defaultProps} />

src/__tests__/VariableSizeGrid.js

@@ -189,6 +189,76 @@ describe('VariableSizeGrid', () => {
       expect(onItemsRendered.mock.calls).toMatchSnapshot();
     });
 
+    it('should scroll to the correct item for align = "auto" at the bottom of the grid', () => {
+      getScrollbarSize.mockImplementation(() => 20);
+
+      const rendered = ReactTestRenderer.create(
+        <VariableSizeGrid {...defaultProps} />
+      );
+      onItemsRendered.mockClear();
+
+      // Scroll down to the last row in the list.
+      rendered
+        .getInstance()
+        .scrollToItem({ columnIndex: 5, rowIndex: 19, align: 'auto' });
+
+      expect(onItemsRendered).toHaveBeenCalledTimes(1);
+      expect(onItemsRendered).toHaveBeenLastCalledWith(
+        expect.objectContaining({
+          visibleRowStartIndex: 18,
+          visibleRowStopIndex: 19,
+        })
+      );
+      // Repeat the previous scrollToItem call.
+      rendered
+        .getInstance()
+        .scrollToItem({ columnIndex: 5, rowIndex: 19, align: 'auto' });
+
+      // Shouldn't have been called again
+      expect(onItemsRendered).toHaveBeenCalledTimes(1);
+      expect(onItemsRendered).toHaveBeenLastCalledWith(
+        expect.objectContaining({
+          visibleRowStartIndex: 18,
+          visibleRowStopIndex: 19,
+        })
+      );
+    });
+
+    it('should scroll to the correct item for align = "auto" at the end of the grid', () => {
+      getScrollbarSize.mockImplementation(() => 20);
+
+      const rendered = ReactTestRenderer.create(
+        <VariableSizeGrid {...defaultProps} width={120} />
+      );
+      onItemsRendered.mockClear();
+
+      // Scroll scross to the last row in the list.
+      rendered
+        .getInstance()
+        .scrollToItem({ columnIndex: 9, rowIndex: 10, align: 'auto' });
+
+      expect(onItemsRendered).toHaveBeenCalledTimes(1);
+      expect(onItemsRendered).toHaveBeenLastCalledWith(
+        expect.objectContaining({
+          visibleColumnStartIndex: 8,
+          visibleColumnStopIndex: 9,
+        })
+      );
+      // Repeat the previous scrollToItem call.
+      rendered
+        .getInstance()
+        .scrollToItem({ columnIndex: 9, rowIndex: 10, align: 'auto' });
+
+      // Shouldn't have been called again
+      expect(onItemsRendered).toHaveBeenCalledTimes(1);
+      expect(onItemsRendered).toHaveBeenLastCalledWith(
+        expect.objectContaining({
+          visibleColumnStartIndex: 8,
+          visibleColumnStopIndex: 9,
+        })
+      );
+    });
+
     it('should scroll to the correct item for align = "start"', () => {
       const rendered = ReactTestRenderer.create(
         <VariableSizeGrid {...defaultProps} />