It would be nice to have this too

[oleedd]

Relational Patterns Currently there are patterns for expressing various types of equality, and kinda an instanceof (for custom matchers against a class). We could express more types of operator-based checks, like:

match(val) {
   when < 10: console.log("small");
   when >= 10 and < 20: console.log("mid");
   default: "large";
}

It would be nice to have this too:

if (val  >= 10 and < 20) console.log("mid");

A similar thing exists in c#.

[ljharb]

if is normal expression space, so adding that ability would need to be its own distinct proposal.

If we're able to add the is operator, though, then you could do if (val is >= 10 and < 20).

[oleedd]

Where is the proposal with the is operator?

[ljharb]

this one. it's the third bullet point in https://github.com/tc39/proposal-pattern-matching?tab=readme-ov-file#specification - but it's not yet clear if we'll be able to keep it or not.