Retire when.js and use async iterators/streams for progressive calls

[oberstet]

Summary

Replace the unmaintained when.js library with modern JavaScript patterns (async iterators/streams) for progressive call results.

Background

Currently, AutobahnJS uses when.js for:

• Full Promises/A+ compliance
• Deferreds (deferred.resolve/reject/notify)
• Progress notifications via deferred.notify()

Progressive call results in WAMP rely on the notify() mechanism, which native Promises don't support.

Current State (v26.1.1)

For release 26.1.1, we're keeping when.js@3.7.8 (the final stable release) to:

• Avoid API breaking changes
• Minimize risk for existing users
• Maintain backward compatibility

Proposed Solution

Replace when.js with async iterators/streams for progressive results:

// Modern async iterator pattern
for await (const chunk of session.callStream("com.example.longop", [args])) {
    console.log("interim result:", chunk);
}
console.log("call completed");

This aligns with modern JavaScript best practices and provides:

• Native browser/Node.js support
• No external dependencies
• Better memory efficiency for streaming results
• Cleaner async/await syntax

API Design Options

Option A: Clean Break (Recommended)

Replace the current .progress() callback pattern entirely with async iterators:

// Old pattern (deprecated)
session.call("proc", [args], {}, {
    onProgress: (chunk) => console.log(chunk)
});

// New pattern
for await (const chunk of session.callStream("proc", [args])) {
    console.log(chunk);
}

Option B: Dual API (Transitional)

Offer both patterns during transition:

• session.call() - returns Promise, supports optional onProgress callback
• session.callStream() - returns async iterator

Then deprecate the callback pattern in a future release.

Implementation Notes

• This is a breaking API change for users relying on progressive results
• Requires documentation updates
• Requires migration guide for existing users
• Consider: Is backward compatibility worth the maintenance burden?

Target

• v26.2.1 or later

References

• MDN: Async iteration
• when.js (unmaintained)
• WAMP progressive call results: https://wamp-proto.org/wamp_latest_ietf.html#name-progressive-call-results

[nouoxu]

Great proposal! Replacing when.js with async iterators/streams is definitely the right direction - it removes external dependencies and aligns with modern JavaScript. Option A (clean break) is probably the better choice long-term. For quick JavaScript prototyping, check out JSBin at https://github.com/nouoxu/jsbin - it's excellent for testing async patterns.