# array.prototype.findlastindex <sup>[![Version Badge][npm-version-svg]][package-url]</sup>

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

This package implements the [es-shim API](https://github.com/es-shims/api) interface. It works in an ES3-supported environment and complies with the proposed [spec](https://tc39.es/proposal-array-find-from-last).

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

```sh
npm install --save array.prototype.findlastindex
```

## Usage/Examples

```js
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);
```

```js
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));
```

```js
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`

[package-url]: https://npmjs.org/package/array.prototype.findlastindex
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[license-url]: LICENSE
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