feat(useSum): new function

packages/math/index.ts

@@ -8,3 +8,4 @@ export * from './useClamp'
 export * from './useFloor'
 export * from './useProjection'
 export * from './useRound'
+export * from './useSum'

packages/math/useSum/index.md

@@ -0,0 +1,16 @@
+---
+category: '@Math'
+---
+
+# useSum
+
+Get the sum of a set of numbers.
+
+## Usage
+
+```ts
+import { useSum } from '@vueuse/math'
+
+const nums = ref([1, 2, 3, 4])
+const sum = useSum(nums)
+```

packages/math/useSum/index.test.ts

@@ -0,0 +1,15 @@
+import { ref } from 'vue-demi'
+import { useSum } from '.'
+
+describe('useSum', () => {
+  it('should be defined', () => {
+    expect(useSum).toBeDefined()
+  })
+  it('should work', () => {
+    const nums = ref([1, 2, 3, 4])
+    const sum = useSum(nums)
+    expect(sum.value).toBe(10)
+    nums.value = [-1, -2, 3, 4]
+    expect(sum.value).toBe(4)
+  })
+})

packages/math/useSum/index.ts

@@ -0,0 +1,18 @@
+import type { ComputedRef } from 'vue-demi'
+import { computed } from 'vue-demi'
+import type { MaybeComputedRef } from '@vueuse/shared'
+import { resolveUnref } from '@vueuse/shared'
+
+/**
+ * Get the sum of a set of numbers.
+ *
+ * @see https://vueuse.org/useSum
+ * @param nums
+ */
+export function useSum(nums: MaybeComputedRef<Array<MaybeComputedRef<number>>>): ComputedRef<number> {
+  return computed(
+    () => resolveUnref(nums).reduce(
+      (prev: number, curr: MaybeComputedRef<number>) => prev + resolveUnref(curr), 0,
+    ),
+  )
+}