feat(watchArray): new function

packages/shared/watchArray/index.md

@@ -0,0 +1,28 @@
+---
+category: Watch
+---
+
+# watchArray
+
+Watch for an array with additions and removals.
+
+## Usage
+
+Similar to `watch`, but provides the added and removed elements to the callback function. Pass `{ deep: true }` if the list is updated in place with `push`, `splice`, etc.
+
+```ts
+import { watchArray } from '@vueuse/core'
+
+const list = ref([1, 2, 3])
+
+watchArray(list, (newList, oldList, added, removed) => {
+  console.log(newList) // [1, 2, 3, 4]
+  console.log(oldList) // [1, 2, 3]
+  console.log(added) // [4]
+  console.log(removed) // []
+})
+
+onMounted(() => {
+  list.value = [...list.value, 4]
+})
+```

packages/shared/watchArray/index.test.ts

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+import { isVue2, nextTick, reactive, ref } from 'vue-demi'
+import { watchArray } from '.'
+
+describe('watchArray', () => {
+  it('should work when two lists are different', async () => {
+    const spy = vitest.fn((newList, oldList, added, removed) => {
+      expect(newList).toEqual([1, 1, 4])
+      expect(oldList).toEqual([1, 2, 3])
+      expect(added).toEqual([1, 4])
+      expect(removed).toEqual([2, 3])
+    })
+
+    const num = ref([1, 2, 3])
+    watchArray(num, spy)
+    num.value = [1, 1, 4]
+    await nextTick()
+    expect(spy).toBeCalledTimes(1)
+  })
+
+  it('should work when two lists are identical', async () => {
+    const spy = vitest.fn((newList, oldList, added, removed) => {
+      expect(newList).toEqual([1, 2, 3])
+      expect(oldList).toEqual([1, 2, 3])
+      expect(added).toEqual([])
+      expect(removed).toEqual([])
+    })
+
+    const num = ref([1, 2, 3])
+    watchArray(num, spy)
+    num.value = [1, 2, 3]
+    await nextTick()
+    expect(spy).toBeCalledTimes(1)
+  })
+
+  it('should work with list push', async () => {
+    const spy = vitest.fn((newList, oldList, added, removed) => {
+      expect(newList).toEqual([1, 2, 3, 4])
+      expect(oldList).toEqual([1, 2, 3])
+      expect(added).toEqual([4])
+      expect(removed).toEqual([])
+    })
+
+    const num = ref([1, 2, 3])
+    watchArray(num, spy, { deep: true })
+    num.value.push(4)
+    await nextTick()
+    // TODO: Vue 2 somehow get trigger twice
+    expect(spy).toBeCalledTimes(isVue2 ? 2 : 1)
+  })
+
+  it('should work with list splice', async () => {
+    const spy = vitest.fn((newList, oldList, added, removed) => {
+      expect(newList).toEqual([1, 5, 6, 7, 3])
+      expect(oldList).toEqual([1, 2, 3])
+      expect(added).toEqual([5, 6, 7])
+      expect(removed).toEqual([2])
+    })
+
+    const num = ref([1, 2, 3])
+    watchArray(num, spy, { deep: true })
+    num.value.splice(1, 1, 5, 6, 7)
+    await nextTick()
+    // TODO: Vue 2 somehow get trigger twice
+    expect(spy).toBeCalledTimes(isVue2 ? 2 : 1)
+  })
+
+  it('should work with reactive source', async () => {
+    const spy = vitest.fn((newList, oldList, added, removed) => {
+      expect(newList).toEqual([1, 2, 3, 4])
+      expect(oldList).toEqual([1, 2, 3])
+      expect(added).toEqual([4])
+      expect(removed).toEqual([])
+    })
+
+    const num = reactive([1, 2, 3])
+    watchArray(num, spy)
+    num.push(4)
+    await nextTick()
+    expect(spy).toBeCalledTimes(1)
+  })
+
+  it('should work with functional source', async () => {
+    const spy = vitest.fn((newList, oldList, added, removed) => {
+      expect(newList).toEqual([1, 2, 3, 4])
+      expect(oldList).toEqual([1, 2, 3])
+      expect(added).toEqual([4])
+      expect(removed).toEqual([])
+    })
+
+    const num = ref([1, 2, 3])
+    watchArray(() => num.value, spy)
+    num.value = [...num.value, 4]
+    await nextTick()
+    expect(spy).toBeCalledTimes(1)
+  })
+})

packages/shared/watchArray/index.ts

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+import type { WatchOptions, WatchSource } from 'vue-demi'
+import { unref, watch } from 'vue-demi'
+
+export declare type WatchArrayCallback<V = any, OV = any> = (value: V, oldValue: OV, added: V, removed: OV, onCleanup: (cleanupFn: () => void) => void) => any
+
+/**
+ * Watch for an array with additions and removals.
+ *
+ * @see https://vueuse.org/watchArray
+ */
+export function watchArray<T, Immediate extends Readonly<boolean> = false>(
+  source: WatchSource<T[]> | T[],
+  cb: WatchArrayCallback<T[], Immediate extends true ? T[] | undefined : T[]>,
+  options?: WatchOptions<Immediate>,
+) {
+  let oldList: T[] = options?.immediate
+    ? []
+    : [...(source instanceof Function
+        ? source()
+        : Array.isArray(source)
+          ? source
+          : unref(source)),
+      ]
+
+  return watch(source as WatchSource<T[]>, (newList, _, onCleanup) => {
+    const oldListRemains = new Array<boolean>(oldList.length)
+    const added: T[] = []
+    for (const obj of newList) {
+      let found = false
+      for (let i = 0; i < oldList.length; i++) {
+        if (!oldListRemains[i] && obj === oldList[i]) {
+          oldListRemains[i] = true
+          found = true
+          break
+        }
+      }
+      if (!found)
+        added.push(obj)
+    }
+    const removed = oldList.filter((_, i) => !oldListRemains[i])
+    cb(newList, oldList, added, removed, onCleanup)
+    oldList = [...newList]
+  }, options)
+}