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<script>

parent.toStringCalled = false;

window.runTest = function() {
    window.onbeforeunload = function(e) {
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        return { toString: function () { parent.toStringCalled = true; return "FAIL"; } };
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    const listener = function(e) {
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        parent.shouldBeTrue("event.defaultPrevented");
        parent.shouldBeEqualToString("event.returnValue", "PASS");
        parent.shouldBeTrue("toStringCalled");
        parent.finishJSTest();
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