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Proxy deleteProperty throws TypeError when returning false #9118

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Proxy deleteProperty throws TypeError when returning false#9118
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@i8-pi
i8-pi
opened on Oct 16, 2016
Contributor
  • Version: v6.8.1
  • Platform: Linux 4.7.6-1-ARCH x86_64 GNU/Linux
  • Subsystem:

When returning false from handler.deleteProperty of a Proxy, a TypeError is thrown

'use strict';
const p = new Proxy({}, { deleteProperty: () => false });
delete p.a;
TypeError: 'deleteProperty' on proxy: trap returned falsish for property 'a'

From my understanding of the Spec, the delete operation should return false (on step 9) instead of throwing an Error.

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bnoordhuis

bnoordhuis commented on Oct 16, 2016

@bnoordhuis
bnoordhuis
on Oct 16, 2016
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Can you report this to V8? From reading the spec I would agree with you that it's a bug but I wonder if the spec itself isn't deficient here. Here is an example of what I mean:

'use strict';
var o = /* either {} or a proxy */;
if (undefined === Object.getOwnPropertyDescriptor(o, 'a'))
  if (false === delete p.a)
    throw Error('uncanny');

With a deleteProperty returning false, you would reach the exception, something that couldn't happen with a regular object (assuming no .a property on the prototype chain) because delete o.undefinedProperty === true.

bnoordhuis
closed this as completedon Oct 16, 2016
bnoordhuis
added
v8 engineIssues and PRs related to the V8 dependency.
on Oct 16, 2016
i8-pi

i8-pi commented on Oct 17, 2016

@i8-pi
i8-pi
on Oct 17, 2016
ContributorAuthor

Not a bug, apparently.
https://bugs.chromium.org/p/v8/issues/detail?id=5523

From the spec quoted in the v8 bug, the delete operator is required to throw if it returns false in strict mode .

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          Proxy deleteProperty throws TypeError when returning false · Issue #9118 · nodejs/node