`JS::Object#await` is unavailable inside Proc converted into JS closure
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Nobody has claimed this yet.
- Dominant language
- Ruby
- Stars
- 875
- Forks
- 68
- Avg merge
- 9d 5h
- Merged PRs (30d)
- 1
Description
Reproducer
<html>
<script src="https://cdn.jsdelivr.net/npm/@ruby/3.3-wasm-wasi@2.6.0/dist/browser.script.iife.js"></script>
<script type="text/ruby" data-eval="async">
require "js"
JS.global.setTimeout(-> {
JS.global[:Promise].resolve.await
}, 0)
</script>
</html>
browser.script.iife.js:2731 Uncaught Error: /bundle/gems/js-2.6.0/lib/js.rb:86:in `await': JS::Object#await can be called only from RubyVM#evalAsync or RbValue#callAsync JS API
If you are using browser.script.iife.js, please ensure that you specify `data-eval="async"` in your script tag
e.g. <script type="text/ruby" data-eval="async">puts :hello</script>
Or <script type="text/ruby" data-eval="async" src="path/to/script.rb"></script> (RuntimeError)
/bundle/gems/js-2.6.0/lib/js.rb:240:in `await'
eval_async:9:in `block in <main>'
at checkStatusTag (browser.script.iife.js:2731:21)
at browser.script.iife.js:2766:11
at wrapRbOperation (browser.script.iife.js:2738:18)
at callRbMethod (browser.script.iife.js:2764:14)
at RbValue.call (browser.script.iife.js:2547:30)
at browser.script.iife.js:2322:38
Workaround
Wrap the block with Fiber.new do ... end.transfer.
JS.global.setTimeout(-> {
Fiber.new do
JS.global[:Promise].resolve.await
end.transfer
}, 0)
Solutions
We have several options to solve the issue
- Always enter the body of Proc in Ruby with
callAsyncinstead ofcall- https://github.com/ruby/ruby.wasm/blob/dc9921a39c42cde001478622058531fc7ebf94e4/packages/npm-packages/ruby-wasm-wasi/src/vm.ts#L101C1-L106C9
- It's no use to manually choose whether
call/callAsyncandeval/evalAsync
- Add conversion method to create an async version of JS function from proc.
- e.g.
JS.global.setTimeout(JS.async do
JS.global[:Promise].resolve.await
end, 0)
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the JS::Object#await reproducer and workaround in this issue, then inspect packages/npm-packages/ruby-wasm-wasi/src/vm.ts around the linked call/callAsync implementation. Compare how Proc callbacks from setTimeout enter Ruby and determine which proposed direction preserves async behavior. Done means the callback can await the Promise without requiring a manual Fiber transfer.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- javascript, ruby, wasm
- Domain
- devtools, web-dev
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100