add array findlastindex

Author: keithamus

src/array-findlastindex.ts

@@ -0,0 +1,31 @@
+export function arrayFindLastIndex<T>(
+  this: T[],
+  pred: (this: T[], value: T, i: number, array: T[]) => boolean,
+  recv = this
+): number {
+  for (let i = this.length; i > 0; i -= 1) {
+    if (pred.call(recv, this[i], i, this)) return i
+  }
+  return -1
+}
+
+/*#__PURE__*/
+export function isSupported(): boolean {
+  return 'findLastIndex' in Array.prototype && typeof Array.prototype.findLastIndex === 'function'
+}
+
+/*#__PURE__*/
+export function isPolyfilled(): boolean {
+  return Array.prototype.findLastIndex === arrayFindLastIndex
+}
+
+export function apply(): void {
+  if (!isSupported()) {
+    const defn = {
+      value: arrayFindLastIndex,
+      writable: true,
+      configurable: true
+    }
+    Object.defineProperty(Array.prototype, 'findLastIndex', defn)
+  }
+}

test/array-findlastindex.js

@@ -0,0 +1,29 @@
+import {apply, arrayFindLastIndex, isPolyfilled, isSupported} from '../lib/array-findlastindex.js'
+
+describe('arrayFindLastIndex', () => {
+  it('has standard isSupported, isPolyfilled, apply API', () => {
+    expect(isSupported).to.be.a('function')
+    expect(isPolyfilled).to.be.a('function')
+    expect(apply).to.be.a('function')
+    expect(isSupported()).to.be.a('boolean')
+    expect(isPolyfilled()).to.equal(false)
+  })
+
+  it('returns value that passes truthy', () => {
+    expect(arrayFindLastIndex.call([1, 2, 3], v => v === 3)).to.equal(2)
+    const arr = [1, 2, 3]
+    const recv = {}
+    expect(
+      arrayFindLastIndex.call(
+        arr,
+        function (v, i, _arr) {
+          // eslint-disable-next-line @typescript-eslint/no-invalid-this
+          expect(this).to.equal(recv)
+          expect(_arr).to.equal(arr)
+          expect(v).to.equal(arr[i])
+        },
+        recv
+      )
+    )
+  })
+})