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fix defineProperty() proxy hook for array length #1911

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fix defineProperty() proxy hook for array length #1911

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f5c34c4
fix defineProperty() proxy hook for array length
farwayer Feb 20, 2026
20d36e5
add regress test
farwayer Mar 4, 2026
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9 changes: 5 additions & 4 deletions lib/VM/JSObject.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1455,10 +1455,11 @@ CallResult<bool> JSObject::putNamedWithReceiver_RJS(
// object/proxy/internal setter, and the property is writable,
// just write into the same slot.

bool isSameObj = *selfHandle == propObj &&
selfHandle.getHermesValue().getRaw() == receiver->getRaw();

if (LLVM_LIKELY(
*selfHandle == propObj &&
selfHandle.getHermesValue().getRaw() == receiver->getRaw() &&
!desc.flags.accessor && !desc.flags.internalSetter &&
isSameObj && !desc.flags.accessor && !desc.flags.internalSetter &&
!desc.flags.hostObject && !desc.flags.proxyObject &&
desc.flags.writable)) {
auto shv = SmallHermesValue::encodeHermesValue(*valueHandle, runtime);
Expand Down Expand Up @@ -1520,7 +1521,7 @@ CallResult<bool> JSObject::putNamedWithReceiver_RJS(
return false;
}

if (*selfHandle == propObj && desc.flags.internalSetter) {
if (isSameObj && desc.flags.internalSetter) {
return internalSetter(
selfHandle, runtime, name, desc, valueHandle, opFlags);
}
Expand Down
30 changes: 30 additions & 0 deletions test/hermes/regress-array-proxy-length.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
/**
* Copyright (c) Meta Platforms, Inc. and affiliates.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*/

// RUN: %hermes -O %s | %FileCheck --match-full-lines %s

print("proxy-length");
// CHECK: proxy-length

let output = [];
let arr = new Proxy([], {
defineProperty(target, property, attributes) {
output.push("def-" + property);
return Reflect.defineProperty(target, property, attributes)
},
deleteProperty(target, property) {
output.push("del-" + property);
return Reflect.deleteProperty(target, property)
},
});

arr.push('a', 'b', 'c')
arr.pop()
arr.shift()
arr.length = 1
print(output);
// CHECK-NEXT: def-0,def-1,def-2,def-length,del-2,def-length,def-0,del-1,def-length,def-length