core-js/modules/esnext.array.last-index.js

'use strict';
var DESCRIPTORS = require('../internals/descriptors');
var addToUnscopables = require('../internals/add-to-unscopables');
var toObject = require('../internals/to-object');
var toLength = require('../internals/to-length');
var defineProperty = require('../internals/object-define-property').f;

// `Array.prototype.lastIndex` getter
// https://github.com/keithamus/proposal-array-last
if (DESCRIPTORS && !('lastIndex' in [])) {
  defineProperty(Array.prototype, 'lastIndex', {
    configurable: true,
    get: function lastIndex() {
      var O = toObject(this);
      var len = toLength(O.length);
      return len == 0 ? 0 : len - 1;
    }
  });

  addToUnscopables('lastIndex');
}