<!DOCTYPE html> <title>onmessageerror content attribute</title> <link rel="author" title="Domenic Denicola" href="mailto:d@domenic.me"> <link rel="help" href="https://html.spec.whatwg.org/multipage/#handler-onmessageerror"> <script src="/resources/testharness.js"></script> <script src="/resources/testharnessreport.js"></script> <body> <script> "use strict"; window.messageErrorHappened = false; function cleanup() { window.messageErrorHappened = false; document.body.removeAttribute("onmessageerror"); } test(() => { assert_equals(document.body.onmessageerror, null, "body"); assert_equals(window.onmessageerror, null, "window"); }, "The default value of onmessageerror is null"); test(t => { t.add_cleanup(cleanup); document.body.setAttribute("onmessageerror", "window.messageErrorHappened = true;") const compiledHandler = document.body.onmessageerror; assert_equals(typeof compiledHandler, "function", "The onmessageerror property must be a function"); compiledHandler(); assert_true(window.messageErrorHappened, "Calling the handler must run the code"); }, "The onmessageerror content attribute must be compiled into the onmessageerror property"); test(t => { t.add_cleanup(cleanup); document.body.setAttribute("onmessageerror", "window.messageErrorHappened = true;") window.dispatchEvent(new Event("messageerror")); assert_true(window.messageErrorHappened, "Dispatching the event must run the code"); }, "The onmessageerror content attribute must execute when an event is dispatched on the window"); </script>