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diff --git a/deps/v8/src/builtins/proxy-prevent-extensions.tq b/deps/v8/src/builtins/proxy-prevent-extensions.tq
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+++ b/deps/v8/src/builtins/proxy-prevent-extensions.tq
@@ -0,0 +1,66 @@
+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include 'src/builtins/builtins-proxy-gen.h'
+
+namespace proxy {
+
+  // ES #sec-proxy-object-internal-methods-and-internal-slots-preventextensions
+  // https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-preventextensions
+  transitioning builtin
+  ProxyPreventExtensions(implicit context: Context)(
+      proxy: JSProxy, doThrow: Boolean): Object {
+    PerformStackCheck();
+    const kTrapName: constexpr string = 'preventExtensions';
+    try {
+      // 1. Let handler be O.[[ProxyHandler]].
+      // 2. If handler is null, throw a TypeError exception.
+      // 3. Assert: Type(handler) is Object.
+      assert(proxy.handler == Null || Is<JSReceiver>(proxy.handler));
+      const handler =
+          Cast<JSReceiver>(proxy.handler) otherwise ThrowProxyHandlerRevoked;
+
+      // 4. Let target be O.[[ProxyTarget]].
+      const target = proxy.target;
+
+      // 5. Let trap be ? GetMethod(handler, "preventExtensions").
+      // 6. If trap is undefined, then (see 6.a below).
+      const trap: Callable = GetMethod(handler, kTrapName)
+          otherwise goto TrapUndefined(target);
+
+      // 7. Let booleanTrapResult be ToBoolean(? Call(trap, handler, «
+      // target»)).
+      const trapResult = Call(context, trap, handler, target);
+
+      // 8. If booleanTrapResult is true, then
+      //    8.a. Let extensibleTarget be ? IsExtensible(target).
+      //    8.b If extensibleTarget is true, throw a TypeError exception.
+      if (BranchIfToBooleanIsTrue(trapResult)) {
+        const extensibleTarget: Object = object::ObjectIsExtensible(target);
+        assert(extensibleTarget == True || extensibleTarget == False);
+        if (extensibleTarget == True) {
+          ThrowTypeError(kProxyPreventExtensionsExtensible);
+        }
+      } else {
+        if (doThrow == True) {
+          ThrowTypeError(kProxyTrapReturnedFalsish, kTrapName);
+        }
+        return False;
+      }
+
+      // 9. Return booleanTrapResult.
+      return True;
+    }
+    label TrapUndefined(target: Object) {
+      // 6.a. Return ? target.[[PreventExtensions]]().
+      if (doThrow == True) {
+        return object::ObjectPreventExtensionsThrow(target);
+      }
+      return object::ObjectPreventExtensionsDontThrow(target);
+    }
+    label ThrowProxyHandlerRevoked deferred {
+      ThrowTypeError(kProxyRevoked, kTrapName);
+    }
+  }
+}  // namespace proxy