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