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Comment by miguelrochefort | Hacker News Reader

The two things miss in TypeScript coming from C#:

Pattern matching:

    if (thing is Person person)
    {
        var name = person.Name
    }

Safe navigation operator:

    var countryName = person.Address?.Country ?? "Unknown";

Type guards are a pain to deal with.

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Lack of the safe navigation operator is a real PITA. You can replace "??" with "||" (more or less), but no solution exists for "?." and I don't know how I lived without it before.

Luckily, we'll probably get it sooner or later [1]. There are also a bunch of typesafe getter function utility libraries that are better than nothing [2-3].

[1] https://github.com/tc39/proposal-optional-chaining

[2] https://github.com/pimterry/typesafe-get

[3] https://github.com/yayoc/optional-chain

Maybe I'm missing something but can't you do this for the second one where countryName will be undefined if it's not set?

    var person = {address:{country:"uk"}}
    var {address: {country: countryName}} = person

That would work, but what if the `Person` type's address can also be null? The following would be an error either at runtime or - in the case of TypeScript - at compile time.

    var person = {address: null}
    var {address: {country: countryName}} = person

Hmm, that's annoying behaviour. This doesn't give a runtime error:

    var [a,b,c] = [1]

Either way, I'd highly recommend just using TypeScript.

Right, because while b and c will be undefined, they are taken from an existing array, not from null/undefined. This will throw

    var [a, b, c] = null

and this (destructing a nested array)

    var [[a]] = []

the point of the "elvis" ?. operator is to make accessing properties _of_ optional values or other optional properties easier.

"Either way, I'd highly recommend just using TypeScript."

Sure, I'd recommend that too, but in this case it "only" helps us by moving the error from runtime to compile-time, nested optional property access remains ugly in the TS world, too. The ?. operator will come to TypeScript as soon as it comes to EcmaScript.

Re safe navigation operator... the idea is to basically port lodash's _.get into an operator, right?

Basically, but with type safety and a decent runtime performance

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