CODEWITHSUNDEEP
typescript
techguy2000
techguy2000

Reputation: 5171

Typescript 'const' assertion on string enum values

I have this enum:

    enum Options {
        Option1 = "xyz",
        Option2 = "abc"
    }

I want to use the values for type checking by creating a union type of 'xyz' | 'abc'. Here is my attempt, but I get this 'const' assertion error:

const validValues = Object.values(Options);
const validKeys = validValues as const;
                  ~~~~~~~~~~~ A 'const' assertion can only be applied to references to
                              enum members, or string, number, boolean, array, or object
                              literals.

What is the proper way to do this?

Upvotes: 3

Views: 4901

Answers (1)

Klas Mellbourn
Klas Mellbourn

Reputation: 44407

You can use the Options enum as a type

enum Options {
        Option1 = "xyz",
        Option2 = "abc"
 }

let validValue: Options
validValue = Options.Option1

console.log(validValue) // xyz

// however, note that this is not allowed
// validValue = 'xyz'

This is another variation, not actually using enums

type Options2 = {
    Option1: 'xyz',
    Option2: 'abc'
}

type keys = keyof Options2 // 'Option1' or 'Option2'
type values = Options2[keys] // 'xyz' or 'abc'

let validValue2: values
validValue2 = 'xyz'
console.log(validValue2) // xyz (duh!)

// this is not allowed
// validValue2 = 'nope'

Upvotes: 1

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