2 var $ = require('../internals/export');
3 var fails = require('../internals/fails');
4 var isArray = require('../internals/is-array');
5 var isObject = require('../internals/is-object');
6 var toObject = require('../internals/to-object');
7 var toLength = require('../internals/to-length');
8 var createProperty = require('../internals/create-property');
9 var arraySpeciesCreate = require('../internals/array-species-create');
10 var arrayMethodHasSpeciesSupport = require('../internals/array-method-has-species-support');
11 var wellKnownSymbol = require('../internals/well-known-symbol');
12 var V8_VERSION = require('../internals/engine-v8-version');
14 var IS_CONCAT_SPREADABLE = wellKnownSymbol('isConcatSpreadable');
15 var MAX_SAFE_INTEGER = 0x1FFFFFFFFFFFFF;
16 var MAXIMUM_ALLOWED_INDEX_EXCEEDED = 'Maximum allowed index exceeded';
18 // We can't use this feature detection in V8 since it causes
19 // deoptimization and serious performance degradation
20 // https://github.com/zloirock/core-js/issues/679
21 var IS_CONCAT_SPREADABLE_SUPPORT = V8_VERSION >= 51 || !fails(function () {
23 array[IS_CONCAT_SPREADABLE] = false;
24 return array.concat()[0] !== array;
27 var SPECIES_SUPPORT = arrayMethodHasSpeciesSupport('concat');
29 var isConcatSpreadable = function (O) {
30 if (!isObject(O)) return false;
31 var spreadable = O[IS_CONCAT_SPREADABLE];
32 return spreadable !== undefined ? !!spreadable : isArray(O);
35 var FORCED = !IS_CONCAT_SPREADABLE_SUPPORT || !SPECIES_SUPPORT;
37 // `Array.prototype.concat` method
38 // https://tc39.github.io/ecma262/#sec-array.prototype.concat
39 // with adding support of @@isConcatSpreadable and @@species
40 $({ target: 'Array', proto: true, forced: FORCED }, {
41 concat: function concat(arg) { // eslint-disable-line no-unused-vars
42 var O = toObject(this);
43 var A = arraySpeciesCreate(O, 0);
45 var i, k, length, len, E;
46 for (i = -1, length = arguments.length; i < length; i++) {
47 E = i === -1 ? O : arguments[i];
48 if (isConcatSpreadable(E)) {
49 len = toLength(E.length);
50 if (n + len > MAX_SAFE_INTEGER) throw TypeError(MAXIMUM_ALLOWED_INDEX_EXCEEDED);
51 for (k = 0; k < len; k++, n++) if (k in E) createProperty(A, n, E[k]);
53 if (n >= MAX_SAFE_INTEGER) throw TypeError(MAXIMUM_ALLOWED_INDEX_EXCEEDED);
54 createProperty(A, n++, E);