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Enum number return type is not type safe #36756
Description
TypeScript Version: 3.8.0-dev.20200211
Search Terms:
Enum return type, enum strictly typing, enum type safety
Code
enum Hello{
world
}
const sayHello = ():Hello => {
return 2;
};
console.log(sayHello()); // 2Expected behavior:
An exception/error that 2 is not one of the enum option
and that i should use the enum and not just a number value. Which in the programming world
is commonly known as Magic number
Actual behavior:
returns 2
Playground Link:
https://www.typescriptlang.org/play/?ssl=1&ssc=1&pln=8&pc=30#code/KYOwrgtgBAEsA28D2BvAsAKClA7kgTvACZQC8UAjJgL6aYDGSIAzgC5TMCGAnnIkmSgAKAJQAuPsjIA+KOixR8wVmHwgoAJgDcNHRkYsk8YADpkAcyFdeCZKJFaoAeieagA
Hackish workaround:
enum Hello{
world = "1",
}
const sayHello = ():Hello => {
return "2"; // <-- will give an error
};
console.log(sayHello()); // 2But typescript should make our code more typesafe and give enums the power it should have in first place.
Activity
AnyhowStep commentedon Feb 12, 2020
Number enums are not really enums at all. It's "by design", even if many people don't agree.
They were originally meant to just be useful aliases for bitmasks.
[Edit]
See: #32690
ismail-codinglab commentedon Feb 12, 2020
Enum numbers are by design meant to be not actually enums and string enums are by design actual enums?
I would just expect number enums to act the same as string enums
Hope you can help me out, it's giving different type restrictions depending on if the Enum is a number or string.
If many people feel the same then it's good to discuss about it
I think you would agree with me that the restrictions for string enums should also be reflected with number / default enums and will help the developer gain a more strictly typed environment
AnyhowStep commentedon Feb 12, 2020
I don't like it, either. It is what it is, though.
But, yes, number and string enums have different behavior. Also, if you look at the JS emit for number and string enums, you'll see that they're also different.
It's worth noting that JS has no actual
enumtype. It's a TS concept. Just likenamespace.I just tell people to not use enums nowadays.
Just do something like,
Or,
It does make the emit uglier, though. In places, you'll see a union type, instead of
MyNumberEnumtypescript-bot commentedon Feb 15, 2020
This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.