From b0ac4fa20191a5b454ac221623dd31b3aceedb40 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Levi=20=28Nguy=E1=BB=85n=20L=C6=B0=C6=A1ng=20Huy=29?=
 <huy.nguyen.luong96@gmail.com>
Date: Sat, 18 Feb 2023 16:39:38 +0700
Subject: [PATCH] feat(useArrayFindLast): new function (#2471)

---
 packages/shared/useArrayFindLast/index.md     | 31 ++++++++++++++
 .../shared/useArrayFindLast/index.test.ts     | 37 +++++++++++++++++
 packages/shared/useArrayFindLast/index.ts     | 40 +++++++++++++++++++
 3 files changed, 108 insertions(+)
 create mode 100644 packages/shared/useArrayFindLast/index.md
 create mode 100644 packages/shared/useArrayFindLast/index.test.ts
 create mode 100644 packages/shared/useArrayFindLast/index.ts

diff --git a/packages/shared/useArrayFindLast/index.md b/packages/shared/useArrayFindLast/index.md
new file mode 100644
index 00000000000..b0584a41c2a
--- /dev/null
+++ b/packages/shared/useArrayFindLast/index.md
@@ -0,0 +1,31 @@
+---
+category: Array
+---
+
+# useArrayFindLast
+
+Reactive `Array.findLast`.
+
+## Usage
+
+```js
+import { useArrayFindLast } from '@vueuse/core'
+
+const list = [ref(1), ref(-1), ref(2)]
+const positive = useArrayFindLast(list, val => val > 0)
+// positive.value: 2
+```
+
+### Use with reactive array
+
+```js
+import { useArrayFindLast } from '@vueuse/core'
+
+const list = reactive([-1, -2])
+const positive = useArrayFindLast(list, val => val > 0)
+// positive.value: undefined
+list.push(10)
+// positive.value: 10
+list.push(5)
+// positive.value: 5
+```
diff --git a/packages/shared/useArrayFindLast/index.test.ts b/packages/shared/useArrayFindLast/index.test.ts
new file mode 100644
index 00000000000..63bf18fd4c5
--- /dev/null
+++ b/packages/shared/useArrayFindLast/index.test.ts
@@ -0,0 +1,37 @@
+import { reactive, ref } from 'vue-demi'
+import { useSetup } from '../../.test'
+import { useArrayFindLast } from '../useArrayFindLast'
+
+describe('useArrayFindLast', () => {
+  it('should be defined', () => {
+    expect(useArrayFindLast).toBeDefined()
+  })
+
+  it('should find positive', () => {
+    useSetup(() => {
+      const item1 = ref(1)
+      const item2 = ref(2)
+      const item3 = ref(3)
+      const positive = useArrayFindLast([item1, item2, item3], val => val > 0)
+      expect(positive.value).toBe(3)
+      item3.value = -1
+      expect(positive.value).toBe(2)
+      item2.value = -1
+      expect(positive.value).toBe(1)
+      item1.value = -1
+      expect(positive.value).toBe(undefined)
+    })
+  })
+
+  it('should work with reactive array', () => {
+    useSetup(() => {
+      const list = reactive([-1, -2])
+      const positive = useArrayFindLast(list, val => val > 0)
+      expect(positive.value).toBe(undefined)
+      list.push(10)
+      expect(positive.value).toBe(10)
+      list.push(5)
+      expect(positive.value).toBe(5)
+    })
+  })
+})
diff --git a/packages/shared/useArrayFindLast/index.ts b/packages/shared/useArrayFindLast/index.ts
new file mode 100644
index 00000000000..18e0d5b105b
--- /dev/null
+++ b/packages/shared/useArrayFindLast/index.ts
@@ -0,0 +1,40 @@
+import type { ComputedRef } from 'vue-demi'
+import { computed } from 'vue-demi'
+import type { MaybeComputedRef } from '../utils'
+import { resolveUnref } from '../resolveUnref'
+
+// Polyfill for node version < 18
+function findLast<T>(arr: T[], cb: (element: T, index: number, array: T[]) => boolean): T | undefined {
+  let index = arr.length
+  while (index-- > 0) {
+    if (cb(arr[index], index, arr))
+      return arr[index]
+  }
+  return undefined
+}
+
+/**
+ * Reactive `Array.findLast`
+ *
+ * @see https://vueuse.org/useArrayFindLast
+ * @param {Array} list - the array was called upon.
+ * @param fn - a function to test each element.
+ *
+ * @returns the last element in the array that satisfies the provided testing function. Otherwise, undefined is returned.
+ */
+export function useArrayFindLast<T>(
+  list: MaybeComputedRef<MaybeComputedRef<T>[]>,
+  fn: (element: T, index: number, array: MaybeComputedRef<T>[]) => boolean,
+): ComputedRef<T | undefined> {
+  return computed(() =>
+    resolveUnref<T | undefined>(
+      // @ts-expect-error - missing in types
+      // https://github.com/microsoft/TypeScript/issues/48829
+      !Array.prototype.findLast
+        ? findLast(resolveUnref(list), (element, index, array) => fn(resolveUnref(element), index, array))
+        : resolveUnref(list)
+          // @ts-expect-error - missing in types
+          .findLast((element, index, array) => fn(resolveUnref(element), index, array)),
+    ),
+  )
+}