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0 pointssanitycheck3y ago0 comments

I found it interesting that I would never use strings this way in JS, but TS seems to encourage it. I definitely would not want to strip typing out of my TS code and try to maintain it as plain JS.

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xsmasher3y ago

What would you use for a field called "stage" that could be set to 'dev' or 'stage' or 'prod'? Or other enum-type things?

I've seen pure JS enums like {'dev' : Symbol('dev'), 'prod' : etc} but I never use them because you can't send them over the wire.

You could use a type like {dev:true} | {prod:true} | {stage:true} but you still wind up comparing strings.

mmis10003y ago

> {dev:true} | {prod:true} | {stage:true}

This can't be accessed safely. Because all value in typescript can be sub type of how it typed.

It means code following will pass.

    var a = { dev: true, get prod() { throw Error() } }
    var b: { dev:true } | {prod:true} | {stage:true} = a

And there is no guarantee that access any of these fields is safe.

xsmasher3y ago

That did not compile for me with my TS settings;

> Type '{ dev: boolean; readonly prod: void; }' is not assignable to type '{ prod: true; }'

It's still a bad solution though; it allows nonsense values like {dev:true, prod:true}.

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xsmasher3y ago

What would you use for a field called "stage" that could be set to 'dev' or 'stage' or 'prod'? Or other enum-type things?

I've seen pure JS enums like {'dev' : Symbol('dev'), 'prod' : etc} but I never use them because you can't send them over the wire.

You could use a type like {dev:true} | {prod:true} | {stage:true} but you still wind up comparing strings.

mmis10003y ago

> {dev:true} | {prod:true} | {stage:true}

This can't be accessed safely. Because all value in typescript can be sub type of how it typed.

It means code following will pass.

    var a = { dev: true, get prod() { throw Error() } }
    var b: { dev:true } | {prod:true} | {stage:true} = a

And there is no guarantee that access any of these fields is safe.

xsmasher3y ago

That did not compile for me with my TS settings;

> Type '{ dev: boolean; readonly prod: void; }' is not assignable to type '{ prod: true; }'

It's still a bad solution though; it allows nonsense values like {dev:true, prod:true}.

1 more reply

j / k navigate · click thread line to collapse