Availability APIs: return "no" or empty string?

[domenic]

Right now a lot of the code looks like

if (capabilities.langaugePairAvailable(...) !== "no") {
  // ...
}

In particular, this will be the common pattern if you are OK accepting either "after-download" or "readily".

There is a clever hack that at least one API uses to make this a bit more ergonomic. Instead of using "no" to signal that you can't do something, use the empty string. Then you can do

if (capabilities.langaugePairAvailable(...)) {
  // ...
}

because the empty string is falsy in JavaScript.

I'm a bit unsure whether we still consider this good practice.

I thought for a bit that maybe TypeScript wouldn't work with this sort of thing but it seems that it does.