Errors / Blocked by the browser

A parser-blocking, cross site (i.e. different eTLD+1) script, …, is invoked via document.write.

A script from another site is added in a way that slows the page, and Chrome may block it on slow connections.

A slower page for everyone, and for visitors on 2G-like connections, a missing script.

Why it happens

• document.write("<script src=…>") for a script on another domain, typical of old ad, analytics and A/B-testing snippets.
• On slow connections Chrome skips such scripts entirely, so they work for you and fail for some visitors.

How to fix it

1. Load the script with a normal <script async src> or by creating the element in code.
2. Ask the vendor for their current snippet: most replaced document.write years ago.
3. To see what a slow connection does to it, set DevTools' Network panel to Slow 3G and reload: Chrome logs a second warning when it skips the script, and whatever that script drew (an ad slot, a test variant, a consent banner) is missing. If the snippet is pasted into a CMS or a tag manager, the fix goes there, not in the theme.

Whose problem it is

Usually another company's script or site, embedded in this one.