While doing the Learn Javascript course the preview browser stopped working at some point, can’t really interact with it, and it doesn’t show any of the changes I make in the code, I’m using Brave, tried to switch to Safari and initially it worked, but after some progress and passing onto the next lessons it stopped working too. The only thing it lets me do is to refresh, and nothing happens.
“Blocked script execution in ‘https://scrimba.com/__sw__blank.html’ because the document’s frame is sandboxed and the ‘allow-scripts’ permission is not set.”
Tried looking around for a fix but It didn’t work, even disabled the “protection” brave offers to try and see if it was blocking JavaScript or something but no luck.
Hey @x1nnas, looks like the support team has picked this up and helping you troubleshoot this. It’s a weird one so not entirely sure what’s causing it. The support team is looping me in to assess it with them so will help you out there.
If we find a solution I’ll update this post for others to see.
Hi José, I had a very similar issue while doing a Scrimba course. I’m using Google Chrome, and the preview browser stopped working too. In my case, the problem was caused by a Chrome extension called “Allow CORS: Access-Control-Allow-Origin”. I disabled it, cleared the browser cache, and everything started working again. Maybe you have a similar extension interfering. Hope this helps!
This error usually means that the embedded preview window (an iframe) Scrimba uses to run your code is being restricted by your browser’s security settings. Specifically, the browser is blocking scripts from running inside a sandboxed iframe because it lacks the allow-scripts permission.
Here’s how you can try to fix it:
Troubleshooting Steps
Switch Browsers: Some users reported this issue on Brave and Safari. Try using Google Chrome or Microsoft Edge, which tend to work better with Scrimba.
Disable Browser Extensions: Especially ones related to privacy, ad-blocking, or CORS (like “Allow CORS: Access-Control-Allow-Origin”)—these can interfere with iframe behavior.
Clear Cache & Cookies: Sometimes stale data causes weird behavior. Clear your browser cache and reload Scrimba.
Use Incognito Mode: This disables most extensions and gives you a clean slate to test if the issue persists.
Restart Your Browser or Device: A classic move, but it often works.
Try a Different Network: Occasionally, network-level restrictions (like firewalls or proxies) can cause this.
My problem was actually resolved by turning off these two extensions:
Troubleshooting Steps
My problem was actually resolved by turning off these two extensions:
At first, I thought the issue was caused by my AdBlocker—but it wasn’t! Still, I recommend trying to disable that extension just in case.