feat: add sumBy

src/index.ts

@@ -78,6 +78,7 @@ export { default as startsWith } from './startsWith'
 export { default as stopEventPropagation } from './stopEventPropagation'
 export { default as storage } from './storage'
 export { default as sum } from './sum'
+export { default as sumBy } from './sumBy'
 export { default as supportPassiveEventListener } from './supportPassiveEventListener'
 export { default as times } from './times'
 export { default as toDate } from './toDate'

src/sumBy.ts

@@ -0,0 +1,13 @@
+/**
+ * 根据 `iteratee` 返回的结果计算传入值的总和。
+ *
+ * @param array 传入的数组
+ * @param iteratee 迭代函数
+ * @returns 总和
+ */
+export default function sumBy<T>(array: T[], iteratee: (item: T) => number): number {
+  return array.reduce<number>((total, item) => {
+    total += iteratee(item)
+    return total
+  }, 0)
+}

test/index.test.ts

@@ -1519,3 +1519,11 @@ describe('sum', () => {
     expect(vtils.sum([4, 2], 8, [6], [])).toBe(20)
   })
 })
+
+describe('sumBy', () => {
+  test('ok', () => {
+    expect(vtils.sumBy([4, 2, 8, 6], item => item)).toBe(20)
+    expect(vtils.sumBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], item => item.n)).toBe(20)
+    expect(vtils.sumBy([vtils.range(0, 10), vtils.range(0, 5)], item => item.length)).toBe(15)
+  })
+})