in operator not working correctly when using Proxy as VM context

Version: v12.13.1
Platform: Windows 10

The in operator does not work correctly when using a Proxy as a VM context.

var o = {};
var p = new Proxy(o, {
    has(target, key) {
        console.log('has', key);
        return Reflect.has(target, key);
    },
    get(target, key, receiver) {
        console.log('get', key);
        return Reflect.get(target, key, receiver);
    },
});
vm.createContext(p);
vm.runInContext(`this.abcInThis = 'abc' in this`, p);
console.log(JSON.stringify(o)); // Prints {"abcInThis":false}

In the above code, the expected output is:

has abc
{"abcInThis":false}

but the actual output is:

get abc
{"abcInThis":true}

If we remove the get(target, key, receiver) function, the still incorrect output is:

{"abcInThis":false}

This is a limitation of V8. See: #22390

I'd be interested in fixing this at some point.

This also causes issues when using the with operator, which prevents merging jsdom/webidl2js#167.

I recently took a pretty deep dive into V8 internals to see what it would take to make fix this issue, and the quick answer is quite a lot. The good news is that V8 will need to update the internal global proxy infrastructure for the proposed realms api when they implement it, which will make it easier to fix this issue.

See also: #17465

Fix event handler ObjectEnvironment instantiation

const vm = require('vm');
var o = {};
var p = new Proxy(o, {
    has(target, key) {
        console.log('has', key);
        return Reflect.has(target, key);
    },
    get(target, key, receiver) {
        console.log('get', key);
        return Reflect.get(target, key, receiver);
    },
});
vm.createContext(p);
vm.runInContext(`this.abcInThis = 'abc' in this`, p);
console.log(JSON.stringify(o)); // Prints {"abcInThis":false}

get abc
{"abcInThis":true}

Still reproducible.

Sorry for the mis-close.

@redyetidev
abcInThis should be false, so this is still reproducible.

Oh yes, I had it backwards, my bad, sorry.

I don't know if we can consider this fixed in Node.js v22 and v24, because:

It prints {"abcInThis":false} as expected
But it doesn't print has abc

This issue has been marked as stale due to 210 days of inactivity.
It will be automatically closed in 30 days if no further activity occurs. If this is still relevant, please leave a comment or update it to keep it open.

/keepalive

This issue has been marked as stale due to 90 days of inactivity.
It will be automatically closed in 30 days if no further activity occurs. If this is still relevant, please leave a comment or update it to keep it open.

/keepalive

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`in` operator not working correctly when using Proxy as VM context #30985

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in operator not working correctly when using Proxy as VM context #30985

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devsnek commented on Dec 16, 2019

ExE-Boss commented on Feb 15, 2020

devsnek commented on Feb 15, 2020

ExE-Boss commented on Feb 16, 2020

avivkeller commented on Jul 11, 2024

ExE-Boss commented on Jul 12, 2024

avivkeller commented on Jul 12, 2024

targos commented on Sep 12, 2025

github-actions commented on Jun 27, 2026

ExE-Boss commented on Jun 28, 2026

github-actions commented on Sep 28, 2026

ExE-Boss commented on Sep 28, 2026

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`in` operator not working correctly when using Proxy as VM context #30985