test/mjsunit/bugs/bug-proto.js

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var realmA = Realm.current();
var realmB = Realm.create();
assertEquals(0, realmA);
assertEquals(1, realmB);

// The global objects match the realms' this binding.
assertSame(this, Realm.global(realmA));
assertSame(Realm.eval(realmB, "this"), Realm.global(realmB));
assertFalse(this === Realm.global(realmB));

// The global object is not accessible cross-realm.
var x = 3;
Realm.shared = this;
assertThrows("Realm.eval(realmB, 'x')");
assertSame(undefined, Realm.eval(realmB, "this.x"));
assertSame(undefined, Realm.eval(realmB, "Realm.shared.x"));

Realm.eval(realmB, "Realm.global(0).y = 1");
assertThrows("y");
assertSame(undefined, this.y);

// Can get or set other objects' properties cross-realm.
var p = {a: 1};
var o = {__proto__: p, b: 2};
Realm.shared = o;
assertSame(1, Realm.eval(realmB, "Realm.shared.a"));
assertSame(2, Realm.eval(realmB, "Realm.shared.b"));

// Cannot get or set a prototype cross-realm.
assertSame(undefined, Realm.eval(realmB, "Realm.shared.__proto__"));

Realm.eval(realmB, "Realm.shared.__proto__ = {c: 3}");
assertSame(1, o.a);
assertSame(undefined, o.c);