es.array.find-index.js

'use strict';
var $ = require('../internals/export');
var arrayMethods = require('../internals/array-methods');
var addToUnscopables = require('../internals/add-to-unscopables');

var internalFindIndex = arrayMethods(6);
var FIND_INDEX = 'findIndex';
var SKIPS_HOLES = true;

// Shouldn't skip holes
if (FIND_INDEX in []) Array(1)[FIND_INDEX](function () { SKIPS_HOLES = false; });

// `Array.prototype.findIndex` method
// https://tc39.github.io/ecma262/#sec-array.prototype.findindex
$({ target: 'Array', proto: true, forced: SKIPS_HOLES }, {
  findIndex: function findIndex(callbackfn /* , that = undefined */) {
    return internalFindIndex(this, callbackfn, arguments.length > 1 ? arguments[1] : undefined);
  }
});

// https://tc39.github.io/ecma262/#sec-array.prototype-@@unscopables
addToUnscopables(FIND_INDEX);