How to safely index with string an object that might be `undefined`?

[round gazelle]

const value = someObject['something'];
// someObject might be `undefined` or of type `{something: string}`

[wild cloak]

there is nothing unsafe about doing someObject['something']

what's unsafe is what you do with value

[round gazelle]

but it doesn't let me

here currentExperiment is that someObject

[wild cloak]

simply make sure currentExperiment isn't undefined

once you know it's not undefined, the you can access the property you want

[round gazelle]

is there a simple way to do that? kind of like someObject?.something but with indexing?

[wild cloak]

you could also do that, yes

there is nothign TypeScript-specific about that

it would be the exact same code in plain JS

[round gazelle]

alright, thanks

[wild cloak]

interface Experiment {
    something: unknown;
}
declare const currentExperiment: Experiment | undefined;

const something = currentExperiment?.something;
// or
if(currentExperiment) currentExperiment.something;

also, as a sidenote, we typically don't prefix interfaces with I in typescript

since there is no difference between an interface, type, class, object at the type level

it's all the same type

[round gazelle]

you see, the first option is good, but the something key can change frequently in my case and i am going to use this at a lot of places in my code. so i want to index it with a constant so that i can change it at one place. and i also don't want it be an if else or ternary otherwise it might get messy.

[round gazelle]

ik, that's something past developers from my team didn't know 🗿

[wild cloak]

you can also do optional chaining with indexed access
someObject?.[someKey]

[wild cloak]

would then make some kind of singleton, or some kind of getter in a module to get the property

[round gazelle]

perfect, thank you.

[wild cloak]

it's vanilla JS btw

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining