robertwb commented on PR #22134:
URL: https://github.com/apache/beam/pull/22134#issuecomment-1180797546
To do this one would have to add methods like flatMap to the Promise
prototype (affecting all Promises across Javascript) or return a subclass
(well, really a hierarchy of subclasses) of Promise (which I looked into and
looks pretty sketchy). This would work if Promise could be a proxy object to
the type it was promising, but it's not.
It looks like another alternative is
```
lines
.invoke("map", (s: string) => s.toLowerCase())
.invoke("flatMap", function* splitWords(line: string) {
yield* line.split(/[^a-z]+/);
})
.invoke("apply", beam.countPerElement())
```
but this is still a bit icky, and looses type safety.
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