Bug 40047

REGRESSION(60409): document.write is not synchronous when using the HTML5 parser It's unclear from the spec: http://www.whatwg.org/specs/web-apps/current-work/multipage/apis-in-html-documents.html#document.write() But it seems to me that document.write() should wait until all parsing is "done" for the write before returning. In the old parser this was not an issue, as it was not as aggressive about yielding. The new HTML5 parser yields when waiting for script loads or for stylesheet loads. http://www.whatwg.org/specs/web-apps/current-work/multipage/scripting-1.html#running-a-script talks about queuing tasks on the task queue, but it doesn't really talk about the parser yielding. The old parser never seems to wait for <script src=""> tags during parsing (in violation of HTML5) nor does it block inline <script> tags ever (which HTML5 says it should for style-sheets), so I think that's how it produces a synchronous document.write behavior.