pub fn async_step(iterator: &Value) -> Result<Value, String>Expand description
One step of a for await loop: return a Promise that settles to a
{value, done} record. For a native async iterator this is iter.next()
(already a promise of the record). For the sync fallback it pops the next raw
value, awaits it, and packages {value: resolved, done:false} (or
{done:true} at exhaustion).