feat(function): tap utility (#1)

Author: innocenzi

src/function.test.ts

@@ -0,0 +1,6 @@
+import { tap } from './function'
+
+it('tap', () => {
+  expect(tap(1, value => value++)).toEqual(1)
+  expect(tap({ a: 1 }, obj => obj.a++)).toEqual({ a: 2 })
+})

src/function.ts

@@ -13,3 +13,20 @@ export function batchInvoke(functions: Nullable<Fn>[]) {
 export function invoke(fn: Fn) {
   return fn()
 }
+
+/**
+ * Pass the value through the callback, and return the value.
+ *
+ * @example
+ * ```
+ * function createUser(name: string): User {
+ *   return tap(new User, user => {
+ *     user.name = name
+ *   })
+ * }
+ * ```
+ */
+export function tap<T>(value: T, callback: (value: T) => void): T {
+  callback(value)
+  return value
+}