feat(useArrayFindLast): new function (#2471)

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
+```

packages/shared/useArrayFindLast/index.test.ts

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+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)
+    })
+  })
+})

packages/shared/useArrayFindLast/index.ts

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+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)),
+    ),
+  )
+}