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  • This WPT test may be referenced by the following Test IDs:
// This tests the issues discussed in https://github.com/whatwg/html/issues/4299
// Note: because browsers do not interoperate on the spec's notion of window reuse (see e.g. https://crbug.com/778318)
// we pick a specific interoperable test case, which is "currently on initial about:blank, but loading something".
async_test(t => {
const iframe = document.createElement("iframe");
// We can't just leave it at the actual initial about:blank because of the interop issues mentioned above.
// So put it in the "currently on initial about:blank, but loading something" state which interoperably does Window
// reuse.
iframe.src = "/common/blank.html";
// Create the Window object. It will be for the initial about:blank since the load of /common/blank.html hasn't
// completed.
document.body.append(iframe);
// Store a string on that Window object so we can later test if it's reused.
iframe.contentWindow.persistedString = "Hello world!";
// This will reset the initial about:blank-ness. But, it will also cancel any ongoing loads.
iframe.contentDocument.open();
// So, re-start the load of /common/blank.html.
iframe.src = "/common/blank.html";
// When the load finally happens, will it reuse the Window object or not?
// Because document.open() resets the initial about:blank-ness, it will *not* reuse the Window object.
// The point of the test is to assert that.
iframe.addEventListener("load", t.step_func_done(() => {
assert_equals(
iframe.contentDocument.URL,
iframe.src,
"Prerequisite check: we are getting the right load event"
);
assert_equals(iframe.contentWindow.persistedString, undefined);
}), { once: true });
}, "document.open() removes the initial about:blank-ness of the document");
// This test is redundant with others in WPT but it's intended to make it clear that document.open() is the
// distinguishing factor. It does the same exact thing but without document.open() and with the resulting final assert
// flipped.
async_test(t => {
const iframe = document.createElement("iframe");
iframe.src = "/common/blank.html";
document.body.append(iframe);
iframe.contentWindow.persistedString = "Hello world!";
// NO document.open() call.
iframe.src = "/common/blank.html";
iframe.addEventListener("load", t.step_func_done(() => {
assert_equals(
iframe.contentDocument.URL,
iframe.src,
"Prerequisite check: we are getting the right load event"
);
assert_equals(iframe.contentWindow.persistedString, "Hello world!");
}), { once: true });
}, "Double-check: without document.open(), Window reuse indeed happens");