2 var DESCRIPTORS = require('../internals/descriptors');
3 var addToUnscopables = require('../internals/add-to-unscopables');
4 var toObject = require('../internals/to-object');
5 var lengthOfArrayLike = require('../internals/length-of-array-like');
6 var defineProperty = require('../internals/object-define-property').f;
8 // `Array.prototype.lastIndex` getter
9 // https://github.com/keithamus/proposal-array-last
10 if (DESCRIPTORS && !('lastIndex' in [])) {
11 defineProperty(Array.prototype, 'lastIndex', {
13 get: function lastIndex() {
14 var O = toObject(this);
15 var len = lengthOfArrayLike(O);
16 return len == 0 ? 0 : len - 1;
20 addToUnscopables('lastIndex');