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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Array.prototype.concat should not modify frozen objects"
href="https://bugs.webkit.org/show_bug.cgi?id=163302">163302</a>
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<th>Summary</th>
<td>Array.prototype.concat should not modify frozen objects
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<th>Classification</th>
<td>Unclassified
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<th>Product</th>
<td>WebKit
</td>
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<th>Version</th>
<td>WebKit Local Build
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<th>Hardware</th>
<td>Unspecified
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<th>OS</th>
<td>Unspecified
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>Normal
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<th>Priority</th>
<td>P2
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<th>Component</th>
<td>JavaScriptCore
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<th>Assignee</th>
<td>webkit-unassigned@lists.webkit.org
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<th>Reporter</th>
<td>mark.lam@apple.com
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<p>
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<pre>The ES6 spec for Array.prototype.concat states that it uses the CreateDataPropertyOrThrow() to add items to the result array. The spec for CreateDataPropertyOrThrow states:
"This abstract operation creates a property whose attributes are set to the same defaults used for properties created by the ECMAScript language assignment operator. Normally, the property will not already exist. If it does exist and is not configurable or if O is not extensible, [[DefineOwnProperty]] will return false causing this operation to throw a TypeError exception."
Since the properties of frozen objects are not extensible nor configurable, Array.prototype.concat should fail to write to the result array if it is frozen.
Ref: <a href="https://tc39.github.io/ecma262/#sec-array.prototype.concat">https://tc39.github.io/ecma262/#sec-array.prototype.concat</a>, <a href="https://tc39.github.io/ecma262/#sec-createdatapropertyorthrow">https://tc39.github.io/ecma262/#sec-createdatapropertyorthrow</a>, and <a href="https://tc39.github.io/ecma262/#sec-createdataproperty">https://tc39.github.io/ecma262/#sec-createdataproperty</a>.</pre>
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