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node_modules/core-js/internals/add-to-unscopables.js

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+'use strict';
+var wellKnownSymbol = require('../internals/well-known-symbol');
+var create = require('../internals/object-create');
+var defineProperty = require('../internals/object-define-property').f;
+
+var UNSCOPABLES = wellKnownSymbol('unscopables');
+var ArrayPrototype = Array.prototype;
+
+// Array.prototype[@@unscopables]
+// https://tc39.es/ecma262/#sec-array.prototype-@@unscopables
+if (ArrayPrototype[UNSCOPABLES] == undefined) {
+  defineProperty(ArrayPrototype, UNSCOPABLES, {
+    configurable: true,
+    value: create(null)
+  });
+}
+
+// add a key to Array.prototype[@@unscopables]
+module.exports = function (key) {
+  ArrayPrototype[UNSCOPABLES][key] = true;
+};