Key in Enum?

[tranquil vector]

Hi there?

Could you help me please. How can I fix this problem?

https://www.typescriptlang.org/play?#code/PTAEEsFsAcHsCcAuBTAJqStUFcA2yAoA5AO20lAEESoBDXAZ1AG8DRQARWAc1AF5QAci7dBAGjagAwrUT8hMxOMkBZWNgbJ5gtRuSCCAXyL45tGpHrbFg0LSbU6jIiAwBPDFjyECp9wDlaSGQALlAGRHhwEl4BQQNfZDkSIOQmAVZ2AG1HS0YAOhEAXTDhHmVs3PoGfMUShVkDYwJwADNQAApzJwgSUBTghgBKFklIN0Dg+QG0rO68oqMCIA

[tawdry oracle]

@tranquil vector Here's a shortened URL of your playground link! You can remove the full link from your message.

Azat S.#0801

Playground Link

Preview:```ts
// imported module

enum Animals {
Dog = 'Dog',
Cat = 'Cat',
Mouse = 'Mouse'
}

let animal = 'Cat' as Animals

// my module

let myName: string = ''

let names = {
[Animals.Dog]: 'Dog',
[Animals.Cat]: 'Cat'
}

if (animal in names) {
myName = names[animal]
...```

You can choose specific lines to embed by selecting them before copying the link.

[ripe quartz]

That's not a bug, the problem is that animal could be Dog | Cat | Mouse, and names could have the property [Animals.Mouse] but nobody told the compiler about it

so it could be [Animals.Mouse]: 4000

which, if typescript didn't throw an error, would be equivalent to
let myName: string = 4000

which is a type error

does that make sense?

[tranquil vector]

Okay. But how can I fix it?

Only like this?

if (animal === Animals.Dog) {
  myName = Animals.Dog
} else if (animal === Animals.Cat) {
  myName = Animals.Cat
}  // ....

[ripe quartz]

yep or use a switch

or just tell typescript to go for it

[tranquil vector]

Sounds sad. Thank you

[ripe quartz]

myName = names[animal as never]

but that turns off the type-system

[ripe quartz]

it's not safe, what you're trying to do, in general

in this specific instance where we can see that names was just created and nothing modifies it, it's easy to prove safe

but that's a rare set of circumstances.

@tranquil vector another way to deal with it

is to derive the type of animal from valid keys of names

[tawdry oracle]

webstrand#8856

Playground Link

Preview:ts ... let animal = "Cat" as keyof typeof names ...