array.prototype.findlastindex

What is array.prototype.findlastindex?

The array.prototype.findlastindex npm package extends the Array prototype to include a findLastIndex method. This method allows you to search an array backwards and find the index of the last element that satisfies a provided testing function. It is particularly useful for finding the last occurrence of elements in arrays where elements may not be unique or when the order of elements is significant.

What are array.prototype.findlastindex's main functionalities?

Finding the last index of an element that satisfies a condition

This feature allows you to find the index of the last element in an array that meets a specific condition. In the provided code sample, the condition is that the element must be greater than 13, which would return 4, the index of 44, as it is the last element satisfying the condition.

[5, 12, 8, 130, 44].findLastIndex(element => element > 13)

Other packages similar to array.prototype.findlastindex

lodash.findlastindex

Lodash is a popular utility library that includes a findLastIndex method. This method offers similar functionality to array.prototype.findlastindex, allowing users to find the index of the last element in an array that satisfies a provided condition. The main difference is that lodash's findLastIndex is a standalone function that takes an array as its first argument, rather than being a method on the array prototype. This can be preferable for those who wish to avoid extending native prototypes or are working in environments where such modifications are discouraged.

README

array.prototype.findlastindex

An ESnext spec-compliant Array.prototype.findLastIndex shim/polyfill/replacement that works as far down as ES3.

This package implements the es-shim API interface. It works in an ES3-supported environment and complies with the proposed spec.

Because Array.prototype.findLastIndex depends on a receiver (the this value), the main export takes the array to operate on as the first argument.

Getting started

npm install --save array.prototype.findlastindex

Usage/Examples

var findLastIndex = require('array.prototype.findlastindex');
var assert = require('assert');

var arr = [1, [2], [], 3, [[4]]];
var isNumber = function (x) { return typeof x === 'number' };

assert.deepEqual(findLastIndex(arr, isNumber), 3);

var findLastIndex = require('array.prototype.findlastindex');
var assert = require('assert');
/* when Array#findLastIndex is not present */
delete Array.prototype.findLastIndex;
var shimmed = findLastIndex.shim();

assert.equal(shimmed, findLastIndex.getPolyfill());
assert.deepEqual(arr.findLastIndex(isNumber), findLastIndex(arr, isNumber));

var findLastIndex = require('array.prototype.findlastindex');
var assert = require('assert');
/* when Array#findLastIndex is present */
var shimmed = findLastIndex.shim();

assert.equal(shimmed, Array.prototype.findLastIndex);
assert.deepEqual(arr.findLastIndex(isNumber), findLastIndex(arr, isNumber));

Tests

Simply clone the repo, npm install, and run npm test

Changelog

v1.2.3 - 2023-08-29

Commits

• [Deps] update define-properties, es-abstract, get-intrinsic 27e8133
• [Tests] add passing test262 test 678edb3
• [Dev Deps] update @es-shims/api, @ljharb/eslint-config, aud, object-inspect, tape 47abe8b
• [Tests] use globalthis 0cf9142