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#4331 — 9.1.9 [[Set]]: super.prop assignment can silently overwrite non-writable properties

• bug_id: 4331
• creation_ts: 2015-04-22 10:14:00 -0700
• short_desc: 9.1.9 [[Set]]: super.prop assignment can silently overwrite non-writable properties
• delta_ts: 2015-10-02 13:14:01 -0700
• product: Draft for 6th Edition
• component: technical issue
• version: Rev 38: April 14, 2015 Final Draft
• rep_platform: All
• op_sys: All
• bug_status: RESOLVED
• resolution: FIXED
• priority: Normal
• bug_severity: critical
• everconfirmed: true
• reporter: Allen Wirfs-Brock
• assigned_to: Allen Wirfs-Brock
• cc: jorendorff

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• commentid: 14317
• comment_count: 0
• who: Allen Wirfs-Brock
• bug_when: 2015-04-22 10:14:16 -0700

see https://esdiscuss.org/topic/super-prop-assignment-can-silently-overwrite-non-writable-properties

If Receiver is different from the object [[Set]] is invoked upon and the property to set already exits as an own property of Receiver, the current algorithm can over-write a non-writable property or turn an accesor property into a data property.

It should fail (return false) in the situation where it currently does either of these.

---

• commentid: 14318
• comment_count: 1
• who: Allen Wirfs-Brock
• bug_when: 2015-04-22 10:16:51 -0700

fixed in rev29 publication draft.

Step 5.e has been updated to read:

5.e. If existingDescriptor is not undefined, then
i. If IsAccessorDescriptor(existingDescriptor) is true, return false.
ii. If existingDescriptor.[[Writable]] is false, return false.
iii. Let valueDesc be the PropertyDescriptor{[[Value]]: V}.
iv. Return Receiver.[[DefineOwnProperty]](P, valueDesc).

the above steps 5.e.i and 5.e.11 are new

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• commentid: 14360
• comment_count: 2
• who: Allen Wirfs-Brock
• bug_when: 2015-04-29 14:32:49 -0700

(In reply to Allen Wirfs-Brock from comment #1)
> fixed in rev29 publication draft.
>

Make that:

fixed in rev39 publication draft.