Weird blank page

[legnaleurc]

Tampermonkey version: BETA v3.12.4708
Chrome 43.0.2357.132 (64-bit)

Please install the following script and visit http://www1.macys.com/shop/product/navy-yard-8-piece-reversible-bedding-ensembles?ID=764254&CategoryID=26795

// ==UserScript==
// @name         My Fancy New Userscript
// @namespace    http://your.homepage/
// @version      0.1
// @description  enter something useful
// @author       You
// @match        http://www1.macys.com/shop/product/navy-yard-8-piece-reversible-bedding-ensembles?ID=764254&CategoryID=26795
// @grant        unsafeWindow
// @run-at       document-start
// ==/UserScript==

for (var i = 0; i < 3; ++i) {
  console.info(document);
}

The page is visually blank.

The weird thing is you have to

1. grant unsafeWindow
2. run-at document-start
3. reference document 3-times or more

If any condition is not matched, then the page renders fine.

[derjanb]

Fixed: http://tampermonkey.net/changelog.php?version=3.12.4712&ext=gcal
Thanks for your bug report.

[devnoname120]

@derjanb Could you please provide us more details about how the bug was fixed (and what did cause it exactly)? I am interested in the technical details. 😃

[derjanb]

Each page gets some Tampermonkey code injected. It consists of two parts, one is located at the Chrome extension context and one directly at the page. Both parts live in a separated world, but they share the DOM. That's why they can use events for communication.

If now document.write is called after the document was closed all event listeners are gone. In order to workaround this TM wraps this function to re-register the event listeners, but this happens only if a userscript uses the document object.

The problem now was that each time the document was referenced by a userscript the write function was wrapped again. Subsequent document.write calls caused multiple event listener (re-)registrations. This caused each TM internal event to be processed multiple times and caused a lot of load.
I'm not sure which of these issues finally broke the page but when I looked at it the body height was far to small. So maybe some code tried to calculate the body height, but failed due to the timing issues caused by TM.

Hope this helped. :)

[devnoname120]

Thank you for the explanations!