feat: add tap

Author: tdreyno

src/__tests__/tap.spec.ts

@@ -0,0 +1,17 @@
+import { PII, tap, unwrap } from "../index"
+
+describe("tap", () => {
+  it("should tap inside PII", () => {
+    const result = PII("TEST_STRING")
+    let b: string | undefined = undefined
+    const mapped = tap(a => (b = a), result)
+    expect(unwrap(mapped)).toBe(b)
+  })
+
+  it("should tap non PII as well", () => {
+    const result = "TEST_STRING"
+    let b: string | undefined = undefined
+    const mapped = tap(a => (b = a), result)
+    expect(unwrap(mapped)).toBe(b)
+  })
+})

src/pii.ts

@@ -40,6 +40,14 @@ export function map<T, T2>(
   return PII(fn(unwrap(item)))
 }
 
+export function tap<T>(fn: (item: T) => void, item: PII<T>): PII<T>
+export function tap<T>(fn: (item: T) => void, item: T): T
+export function tap<T>(fn: (item: T) => void, item: PII<T> | T): PII<T> | T {
+  fn(unwrap(item))
+
+  return item
+}
+
 export function test<T>(fn: (item: T) => boolean, item: PII<T>): boolean
 export function test<T>(fn: (item: T) => boolean, item: T): boolean
 export function test<T>(fn: (item: T) => boolean, item: PII<T> | T): boolean {