feat(core): add index, nth and last helpers

Author: tdreyno

src/__tests__/index.spec.ts

@@ -0,0 +1,11 @@
+import { index } from "../index"
+
+describe("index", () => {
+  test("gets the index item in an array", () => {
+    expect(index(0)([0, 1])).toBe(0)
+  })
+
+  test("gets the index item in an empty array", () => {
+    expect(index(0)([])).toBe(undefined)
+  })
+})

src/__tests__/last.spec.ts

@@ -0,0 +1,11 @@
+import { last } from "../index"
+
+describe("last", () => {
+  test("gets the last item in an array", () => {
+    expect(last([0, 1])).toBe(1)
+  })
+
+  test("gets the last item in an empty array", () => {
+    expect(last([])).toBe(undefined)
+  })
+})

src/__tests__/nth.spec.ts

@@ -0,0 +1,11 @@
+import { nth } from "../index"
+
+describe("nth", () => {
+  test("gets the nth item in an array", () => {
+    expect(nth(1)([0, 1])).toBe(0)
+  })
+
+  test("gets the nth item in an empty array", () => {
+    expect(nth(1)([])).toBe(undefined)
+  })
+})

src/index.ts

@@ -1,5 +1,11 @@
 /* eslint-disable @typescript-eslint/no-explicit-any */
-export const first = <T>(items: T[]): T => items[0]
+export const index = (i: number) => <T>(items: T[]): T => items[i]
+
+export const nth = (n: number) => index(n - 1)
+
+export const first = index(0)
+
+export const last = <T>(items: T[]): T => items[items.length - 1]
 
 export const constant = <T>(value: T) => () => value