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- 'use strict';
- var $ = require('../internals/export');
- var fails = require('../internals/fails');
- var isArray = require('../internals/is-array');
- var isObject = require('../internals/is-object');
- var toObject = require('../internals/to-object');
- var lengthOfArrayLike = require('../internals/length-of-array-like');
- var doesNotExceedSafeInteger = require('../internals/does-not-exceed-safe-integer');
- var createProperty = require('../internals/create-property');
- var arraySpeciesCreate = require('../internals/array-species-create');
- var arrayMethodHasSpeciesSupport = require('../internals/array-method-has-species-support');
- var wellKnownSymbol = require('../internals/well-known-symbol');
- var V8_VERSION = require('../internals/environment-v8-version');
-
- var IS_CONCAT_SPREADABLE = wellKnownSymbol('isConcatSpreadable');
-
- // We can't use this feature detection in V8 since it causes
- // deoptimization and serious performance degradation
- // https://github.com/zloirock/core-js/issues/679
- var IS_CONCAT_SPREADABLE_SUPPORT = V8_VERSION >= 51 || !fails(function () {
- var array = [];
- array[IS_CONCAT_SPREADABLE] = false;
- return array.concat()[0] !== array;
- });
-
- var isConcatSpreadable = function (O) {
- if (!isObject(O)) return false;
- var spreadable = O[IS_CONCAT_SPREADABLE];
- return spreadable !== undefined ? !!spreadable : isArray(O);
- };
-
- var FORCED = !IS_CONCAT_SPREADABLE_SUPPORT || !arrayMethodHasSpeciesSupport('concat');
-
- // `Array.prototype.concat` method
- // https://tc39.es/ecma262/#sec-array.prototype.concat
- // with adding support of @@isConcatSpreadable and @@species
- $({ target: 'Array', proto: true, arity: 1, forced: FORCED }, {
- // eslint-disable-next-line no-unused-vars -- required for `.length`
- concat: function concat(arg) {
- var O = toObject(this);
- var A = arraySpeciesCreate(O, 0);
- var n = 0;
- var i, k, length, len, E;
- for (i = -1, length = arguments.length; i < length; i++) {
- E = i === -1 ? O : arguments[i];
- if (isConcatSpreadable(E)) {
- len = lengthOfArrayLike(E);
- doesNotExceedSafeInteger(n + len);
- for (k = 0; k < len; k++, n++) if (k in E) createProperty(A, n, E[k]);
- } else {
- doesNotExceedSafeInteger(n + 1);
- createProperty(A, n++, E);
- }
- }
- A.length = n;
- return A;
- }
- });
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