add findLastIndex for array

Author: smaillz

src/array/__tests__/findLastIndex.ts

@@ -0,0 +1,22 @@
+import findLastIndex from '../findLastIndex';
+
+describe('utils/array/findLastIndex', () => {
+    it('should return founded value or undefined otherwise', () => {
+        const arr = [1, 2, 3, 4, 5, 4, 3, 2, 1];
+
+        expect(findLastIndex((a) => a > 3, arr)).toBe(5);
+        expect(findLastIndex((a) => a > 100, arr)).toBe(-1);
+        expect(findLastIndex<number>((a) => a % 2 === 0)(arr)).toBe(7);
+    });
+
+    it('test callback parameters', () => {
+        const fn = jest.fn();
+        const arr = [1, 2, 3];
+
+        findLastIndex(fn, arr);
+
+        expect(fn).toHaveBeenCalledWith(3, 2, arr);
+        expect(fn).toHaveBeenCalledWith(2, 1, arr);
+        expect(fn).toHaveBeenCalledWith(1, 0, arr);
+    });
+});

src/array/findLastIndex.ts

@@ -0,0 +1,31 @@
+import curryN from '../function/curryN';
+import { ArrPred } from '../typings/types';
+
+interface FindLastIndex {
+    <T>(fn: ArrPred<T>, list: ArrayLike<T>): number;
+    <T>(fn: ArrPred<T>): (list: ArrayLike<T>) => number;
+}
+
+/**
+ * Returns the index of the last element of the list which matches the
+ * predicate, or `-1` if no element matches.
+ *
+ * @param {Function} fn The predicate function used to determine if the element is the
+ * desired one.
+ * @param {Array} arr The array to consider.
+ * @return {Number} The index of the element found, or `-1`.
+ * @example
+ *
+ *      var xs = [{a: 1}, {a: 2}, {a: 3}, {a: 2}, {a: 1}];
+ *      findLastIndex(x => x.a === 2)(xs); //=> 3
+ *      findLastIndex(x => x.a === 4)(xs); //=> -1
+ */
+export default curryN(2, <T>(fn: ArrPred<T>, arr: ArrayLike<T> = []) => {
+    for (let i = arr.length - 1; i >= 0; i--) {
+        if (fn(arr[i], i, arr)) {
+            return i;
+        }
+    }
+
+    return -1;
+}) as FindLastIndex;