Uses document.write()
Using document.write()
can delay the display of page content by tens of seconds
and is particularly problematic for users on slow connections.
Chrome therefore blocks the execution of document.write() in many cases,
meaning you can't rely on it.
How the Lighthouse document.write() audit fails
Lighthouse flags
calls to document.write() that weren't blocked by Chrome:
For the most problematic uses,
Chrome will either block calls to document.write()
or emit a console warning about them, depending on the user's connection speed.
Either way, the affected calls appear in the DevTools Console.
See Google's Intervening against document.write()
article for more information.
Lighthouse reports any remaining calls to document.write()
because it adversely affects performance no matter how it's used,
and there are better alternatives.
Each Best Practices audit is weighted equally in the Lighthouse Best Practices Score. Learn more in The Best Practices score.
Avoid document.write()
Remove all uses of document.write() in your code. If it's being used
to inject third-party scripts, try using
asynchronous loading
instead.
If third-party code is using document.write(),
ask the provider to support asynchronous loading.
Resources
- Source code for Uses
document.write()audit - Intervening against
document.write() - Parser blocking versus asynchronous JavaScript