Heads up! This blog post hasn't been updated in over 2 years. CodePen is an ever changing place, so if this post references features, you're probably better off checking the docs. Get in touch with support if you have further questions.

Accidentally create an Pen that hangs? (e.g. a JS infinite loop). That can be a pretty frustrating experience because you can’t even fix the problem before the browser hangs or crashes.

We have a solution for that now. Add ?turn_off_js=true to the URL and the JavaScript for that Pen won’t run. This means you can fix the problem and re-save the Pen and then remove the URL parameter and try it again. This also works on any page with a grid of Pen previews, like your profile page, meaning you can delete the Pen from there as well if needed. JavaScript still runs on the parent page, making these things possible, just not in the Pen itself.

Documentation on this feature here.