I tried to reproduce this problem on macOS 26.2 (25C56) and iPadOS 26.2 (23C55) using Xcode 26.2 (17C52) and I was unable to reproduce this problem. For the very simple case I tried I'm seeing JavaScript execution times ~3-5ms, nothing near a full second. I'm interested in seeing if you're doing anything different than the sample I created. If you can provide a reproducible test case, maybe consider opening a code level support request (https://developer.apple.com/support/technical/).
Topic:
Safari & Web
SubTopic:
General
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