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node_modules/core-js/modules/es.array.concat.js

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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/engine-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;
+  }
+});