feat: Update Accordion expansion behavior

src/components/Accordion/Accordion.test.tsx

@@ -279,9 +279,22 @@ describe('Accordion component', () => {
       },
     ]
 
-    it('shows the expanded items by default', () => {
+    it('shows one expanded item when multiselectable is false', () => {
       const { getByTestId } = render(<Accordion items={testExpandedItems} />)
 
+      // The last expanded item "wins" if multiple new items have expanded:true
+      expect(getByTestId(`accordionItem_${testItems[0].id}`)).not.toBeVisible()
+      expect(getByTestId(`accordionItem_${testItems[1].id}`)).not.toBeVisible()
+      expect(getByTestId(`accordionItem_${testItems[2].id}`)).not.toBeVisible()
+      expect(getByTestId(`accordionItem_${testItems[3].id}`)).not.toBeVisible()
+      expect(getByTestId(`accordionItem_${testItems[4].id}`)).toBeVisible()
+    })
+
+    it('shows all expanded items when multiselectable is true', () => {
+      const { getByTestId } = render(
+        <Accordion multiselectable items={testExpandedItems} />
+      )
+
       expect(getByTestId(`accordionItem_${testItems[0].id}`)).not.toBeVisible()
       expect(getByTestId(`accordionItem_${testItems[1].id}`)).toBeVisible()
       expect(getByTestId(`accordionItem_${testItems[2].id}`)).not.toBeVisible()
@@ -399,4 +412,96 @@ describe('Accordion component', () => {
       expect(customToggleFunction).toHaveBeenCalledOnce()
     })
   })
+
+  describe('when new items are added', () => {
+    let oldItems: AccordionItemProps[]
+    let newItems: AccordionItemProps[]
+
+    beforeEach(() => {
+      oldItems = testItems.slice(0, 2).map((item) => ({ ...item }))
+      newItems = testItems.slice(2).map((item) => ({ ...item }))
+    })
+
+    it('renders new items', () => {
+      const { getByTestId, rerender } = render(<Accordion items={oldItems} />)
+      rerender(<Accordion items={[...oldItems, ...newItems]} />)
+      expect(getByTestId(`accordionItem_${oldItems[0].id}`)).toBeInTheDocument()
+      expect(getByTestId(`accordionItem_${oldItems[1].id}`)).toBeInTheDocument()
+      expect(getByTestId(`accordionItem_${newItems[0].id}`)).toBeInTheDocument()
+      expect(getByTestId(`accordionItem_${newItems[1].id}`)).toBeInTheDocument()
+      expect(getByTestId(`accordionItem_${newItems[2].id}`)).toBeInTheDocument()
+    })
+
+    describe('when multiselectable is false', () => {
+      it('maintains existing expansion if new unexpanded items are added', () => {
+        const { getByText, getByTestId, rerender } = render(
+          <Accordion items={oldItems} />
+        )
+        fireEvent.click(getByText(oldItems[1].title as string))
+
+        rerender(<Accordion items={[...oldItems, ...newItems]} />)
+        expect(getByTestId(`accordionItem_${oldItems[0].id}`)).not.toBeVisible()
+        expect(getByTestId(`accordionItem_${oldItems[1].id}`)).toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[0].id}`)).not.toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[1].id}`)).not.toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[2].id}`)).not.toBeVisible()
+      })
+
+      it('collapses existing expansion if new expanded items are added', () => {
+        const { getByText, getByTestId, rerender } = render(
+          <Accordion items={oldItems} />
+        )
+        fireEvent.click(getByText(oldItems[1].title as string))
+
+        // The last expanded item "wins" if multiple new items have expanded:true
+        newItems[0].expanded = true
+        newItems[1].expanded = true
+        rerender(<Accordion items={[...oldItems, ...newItems]} />)
+        expect(getByTestId(`accordionItem_${oldItems[0].id}`)).not.toBeVisible()
+        expect(getByTestId(`accordionItem_${oldItems[1].id}`)).not.toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[0].id}`)).not.toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[1].id}`)).toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[2].id}`)).not.toBeVisible()
+      })
+    })
+
+    describe('when multiselectable is true', () => {
+      it('maintains existing expansions if new unexpanded items are added', () => {
+        const { getByText, getByTestId, rerender } = render(
+          <Accordion multiselectable items={oldItems} />
+        )
+        fireEvent.click(getByText(oldItems[0].title as string))
+        fireEvent.click(getByText(oldItems[1].title as string))
+
+        rerender(
+          <Accordion multiselectable items={[...oldItems, ...newItems]} />
+        )
+        expect(getByTestId(`accordionItem_${oldItems[0].id}`)).toBeVisible()
+        expect(getByTestId(`accordionItem_${oldItems[1].id}`)).toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[0].id}`)).not.toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[1].id}`)).not.toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[2].id}`)).not.toBeVisible()
+      })
+
+      it('maintains existing expansions if new expanded items are added', () => {
+        const { getByText, getByTestId, rerender } = render(
+          <Accordion multiselectable items={oldItems} />
+        )
+        fireEvent.click(getByText(oldItems[0].title as string))
+        fireEvent.click(getByText(oldItems[1].title as string))
+
+        // The last expanded item "wins" if multiple new items have expanded:true
+        newItems[1].expanded = true
+        newItems[2].expanded = true
+        rerender(
+          <Accordion multiselectable items={[...oldItems, ...newItems]} />
+        )
+        expect(getByTestId(`accordionItem_${oldItems[0].id}`)).toBeVisible()
+        expect(getByTestId(`accordionItem_${oldItems[1].id}`)).toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[0].id}`)).not.toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[1].id}`)).toBeVisible()
+        expect(getByTestId(`accordionItem_${newItems[2].id}`)).toBeVisible()
+      })
+    })
+  })
 })

src/components/Accordion/Accordion.tsx

@@ -62,16 +62,44 @@ export const AccordionItem = ({
   )
 }
 
+function buildExpansions(
+  items: AccordionItemProps[],
+  multiselectable: boolean,
+  savedExpansions = new Map<string, boolean | undefined>()
+) {
+  const lastExpandedItem = items.findLast(
+    (item) => item.expanded || savedExpansions.get(item.id)
+  )
+  return items.reduce((map, item) => {
+    map.set(
+      item.id,
+      !multiselectable
+        ? !!lastExpandedItem && item.id === lastExpandedItem.id
+        : (savedExpansions.get(item.id) ?? !!item.expanded)
+    )
+    return map
+  }, new Map<string, boolean | undefined>())
+}
+
 export const Accordion = ({
   bordered,
   items,
   className,
   multiselectable = false,
 }: AccordionProps): JSX.Element => {
-  const [openItems, setOpenState] = useState(
-    items.filter((i) => !!i.expanded).map((i) => i.id)
+  const [savedExpansions, setSavedExpansions] = useState(
+    buildExpansions(items, multiselectable)
   )
 
+  // Update saved expansions with new items as the appear
+  const [prevItems, setPrevItems] = useState(items)
+  if (items !== prevItems) {
+    setPrevItems(items)
+    setSavedExpansions((prevExpansions) =>
+      buildExpansions(items, multiselectable, prevExpansions)
+    )
+  }
+
   const classes = classnames(
     'usa-accordion',
     {
@@ -81,21 +109,18 @@ export const Accordion = ({
   )
 
   const toggleItem = (itemId: AccordionItemProps['id']): void => {
-    const newOpenItems = [...openItems]
-    const itemIndex = openItems.indexOf(itemId)
-    const isMultiselectable = multiselectable
-
-    if (itemIndex > -1) {
-      newOpenItems.splice(itemIndex, 1)
-    } else {
-      if (isMultiselectable) {
-        newOpenItems.push(itemId)
+    setSavedExpansions((prevExpansions) => {
+      const updatedExpansions = new Map(prevExpansions)
+      if (updatedExpansions.get(itemId)) {
+        updatedExpansions.set(itemId, false)
       } else {
-        newOpenItems.splice(0, newOpenItems.length)
-        newOpenItems.push(itemId)
+        if (!multiselectable) {
+          updatedExpansions.forEach((_val, key, map) => map.set(key, false))
+        }
+        updatedExpansions.set(itemId, true)
       }
-    }
-    setOpenState(newOpenItems)
+      return updatedExpansions
+    })
   }
 
   return (
@@ -107,7 +132,7 @@ export const Accordion = ({
         <AccordionItem
           key={`accordionItem_${i}`}
           {...item}
-          expanded={openItems.indexOf(item.id) > -1}
+          expanded={savedExpansions.get(item.id) ?? false}
           handleToggle={(e): void => {
             if (item.handleToggle) item.handleToggle(e)
             toggleItem(item.id)