From 25f6e30f17953bf6f4d5f6fe421aef1d5574b4bf Mon Sep 17 00:00:00 2001
From: Nikola Begedin <begedinnikola@gmail.com>
Date: Wed, 4 Jan 2023 20:15:23 +0100
Subject: [PATCH] fix(useVirtualList): List sometimes missing elements (#2477)

* FIX 2065: List sometimes missing elements

Add tests

* Fix import

* Undo change + fix tests

* Contrain PR to only the single bugfix

* Undo formatting change

* Undo formatting change

Co-authored-by: wheat <jacobrclevenger@gmail.com>
---
 packages/core/useVirtualList/index.test.ts | 114 +++++++++++++++++++++
 packages/core/useVirtualList/index.ts      |  13 ++-
 2 files changed, 120 insertions(+), 7 deletions(-)
 create mode 100644 packages/core/useVirtualList/index.test.ts

diff --git a/packages/core/useVirtualList/index.test.ts b/packages/core/useVirtualList/index.test.ts
new file mode 100644
index 00000000000..17b514d5736
--- /dev/null
+++ b/packages/core/useVirtualList/index.test.ts
@@ -0,0 +1,114 @@
+import { ref } from 'vue-demi'
+import { useVirtualList } from '.'
+
+describe('useVirtualList', () => {
+  it('should be defined', () => {
+    expect(useVirtualList).toBeDefined()
+  })
+})
+
+describe('useVirtualList, vertical', () => {
+  it('returns all original items if they fit the container', () => {
+    const {
+      list,
+      containerProps: { ref: containerRef },
+      scrollTo,
+    } = useVirtualList(ref(['a', 'b', 'c', 'd', 'e', 'f']), { itemHeight: () => 50, overscan: 1 })
+    const div = { ...document.createElement('div'), clientHeight: 50 }
+
+    containerRef.value = div
+
+    containerRef.value = { ...div, clientHeight: 200 }
+    scrollTo(0)
+    expect(list.value.map(i => i.data)).toEqual(['a', 'b', 'c', 'd', 'e', 'f'])
+
+    containerRef.value = { ...div, clientHeight: 250 }
+    scrollTo(0)
+    expect(list.value.map(i => i.data)).toEqual(['a', 'b', 'c', 'd', 'e', 'f'])
+  })
+
+  it('returns the current visible window of items if there are too many for the container', () => {
+    const {
+      list,
+      containerProps: { ref: containerRef },
+      scrollTo,
+    } = useVirtualList(ref(['a', 'b', 'c', 'd', 'e', 'f', 'g']), { itemHeight: () => 50, overscan: 1 })
+    const div = { ...document.createElement('div'), clientHeight: 50 }
+
+    containerRef.value = div
+
+    scrollTo(0)
+    expect(list.value.map(i => i.data)).toEqual(['a', 'b', 'c'])
+
+    scrollTo(1)
+    expect(list.value.map(i => i.data)).toEqual(['a', 'b', 'c'])
+
+    scrollTo(2)
+    expect(list.value.map(i => i.data)).toEqual(['b', 'c', 'd'])
+
+    scrollTo(3)
+    expect(list.value.map(i => i.data)).toEqual(['c', 'd', 'e'])
+
+    scrollTo(4)
+    expect(list.value.map(i => i.data)).toEqual(['d', 'e', 'f'])
+
+    scrollTo(5)
+    expect(list.value.map(i => i.data)).toEqual(['e', 'f', 'g'])
+
+    scrollTo(6)
+    expect(list.value.map(i => i.data)).toEqual(['f', 'g'])
+  })
+})
+
+describe('useVirtualList, horizontal', () => {
+  it('returns all original items if they fit the container', () => {
+    const {
+      list,
+      containerProps: { ref: containerRef },
+      scrollTo,
+    } = useVirtualList(ref(['a', 'b', 'c', 'd', 'e', 'f']), { itemWidth: () => 50, overscan: 1 })
+    const div = { ...document.createElement('div'), clientWidth: 50 }
+
+    containerRef.value = div
+
+    containerRef.value = { ...div, clientWidth: 200 }
+    scrollTo(0)
+    expect(list.value.map(i => i.data)).toEqual(['a', 'b', 'c', 'd', 'e', 'f'])
+
+    containerRef.value = { ...div, clientWidth: 250 }
+    scrollTo(0)
+    expect(list.value.map(i => i.data)).toEqual(['a', 'b', 'c', 'd', 'e', 'f'])
+  })
+
+  it('returns the current visible window of items if there are too many for the container', () => {
+    const {
+      list,
+      containerProps: { ref: containerRef },
+      scrollTo,
+    } = useVirtualList(ref(['a', 'b', 'c', 'd', 'e', 'f', 'g']), { itemWidth: () => 50, overscan: 1 })
+    const div = { ...document.createElement('div'), clientWidth: 50 }
+
+    containerRef.value = div
+
+    scrollTo(0)
+    expect(list.value.map(i => i.data)).toEqual(['a', 'b', 'c'])
+
+    scrollTo(1)
+    expect(list.value.map(i => i.data)).toEqual(['a', 'b', 'c'])
+
+    scrollTo(2)
+    expect(list.value.map(i => i.data)).toEqual(['b', 'c', 'd'])
+
+    scrollTo(3)
+    expect(list.value.map(i => i.data)).toEqual(['c', 'd', 'e'])
+
+    scrollTo(4)
+    expect(list.value.map(i => i.data)).toEqual(['d', 'e', 'f'])
+
+    scrollTo(5)
+    expect(list.value.map(i => i.data)).toEqual(['e', 'f', 'g'])
+
+    scrollTo(6)
+    expect(list.value.map(i => i.data)).toEqual(['f', 'g'])
+  })
+})
diff --git a/packages/core/useVirtualList/index.ts b/packages/core/useVirtualList/index.ts
index 42b3e22c1be..c0656b83d87 100644
--- a/packages/core/useVirtualList/index.ts
+++ b/packages/core/useVirtualList/index.ts
@@ -120,20 +120,19 @@ function useVirtualListResources<T>(list: MaybeRef<T[]>): UseVirtualListResource
 }
 
 function createGetViewCapacity<T>(state: UseVirtualListResources<T>['state'], source: UseVirtualListResources<T>['source'], itemSize: UseVirtualListItemSize) {
-  return (containerHeight: number) => {
+  return (containerSize: number) => {
     if (typeof itemSize === 'number')
-      return Math.ceil(containerHeight / itemSize)
+      return Math.ceil(containerSize / itemSize)
 
     const { start = 0 } = state.value
     let sum = 0
     let capacity = 0
     for (let i = start; i < source.value.length; i++) {
-      const height = itemSize(i)
-      sum += height
-      if (sum >= containerHeight) {
-        capacity = i
+      const size = itemSize(i)
+      sum += size
+      capacity = i
+      if (sum > containerSize)
         break
-      }
     }
     return capacity - start
   }