Allow JIT fast-path on Cloudflare Workers when new Function is available and gracefully fallback
#5462
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−16
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mhart
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Nov 19, 2025
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| const ua = typeof navigator === "undefined" ? undefined : navigator?.userAgent; | ||
| const isCloudflare = typeof ua === "string" && ua.includes("Cloudflare"); | ||
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| if (isCloudflare) { | ||
| // Cloudflare Workers can vary by compat flag; always re-check. | ||
| return canUseFunction(); | ||
| } |
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Can check for this directly:
if (globalThis.Cloudflare?.compatibilityFlags?.allow_eval_during_startup)
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Ah wait – I think I see the problem – even if that flag's enabled, this check might happen at a time other than startup... so you have to check regardless, and can't cache... right?
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Cloudflare Workers now permit new Function at module scope, so this removes the blanket disable and rechecks
evalavailability each time on Cloudflare. This PR has no changes to non-workerd JS runtimes.When the fast path can compile and run, Workers get the JIT speedup; if Function is blocked (compat flag or runtime error), parsing quietly falls back to the slow path.