Common issues

componentize-js 0.19.3 fallback

Symptom

While running jco componentize, you may see a warning like this:

warning Falling back to componentize-js 0.19.3 because this component requests Preview 2 WASI packages older than 0.2.10.

If that component is then run on newer Wasmtime releases, especially Wasmtime 42 or newer, you may hit the same isolate crash that was fixed upstream in componentize-js 0.20.0.

Root cause

jco normally uses componentize-js 0.20.0 or newer, which includes the upstream fix for ComponentizeJS issue #224.

When the component’s WIT still depends on Preview 2 WASI packages older than 0.2.10, jco must fall back to componentize-js 0.19.3 for compatibility. In practice this usually shows up as wasi:http older than 0.2.10, but related dependencies such as wasi:clocks, wasi:random, and wasi:io can force the same fallback. The older componentize-js version does not include the upstream fix, so the crash can reappear.

For background, see jco issue #1415.

Solution

Update wasi:http and any related Preview 2 WASI dependencies to 0.2.10 or newer, then re-run jco componentize.

If you manage your WIT dependencies with wkg, fetching the updated packages can look like this:

wkg get --format wit wasi:http@0.2.10
wkg get --format wit wasi:clocks@0.2.10
wkg get --format wit wasi:random@0.2.10
wkg get --format wit wasi:io@0.2.10

After updating the packages, make sure your entry WIT file and any vendored dependency files reference the newer versions before componentizing again.