[Webkit-unassigned] [Bug 163302] New: Array.prototype.concat should not modify frozen objects

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=163302

            Bug ID: 163302
           Summary: Array.prototype.concat should not modify frozen
                    objects
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Local Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mark.lam at apple.com

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: https://tc39.github.io/ecma262/#sec-array.prototype.concat, https://tc39.github.io/ecma262/#sec-createdatapropertyorthrow, and https://tc39.github.io/ecma262/#sec-createdataproperty.

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