CODEWITHSUNDEEP
typescript
Lirik Keltran
Lirik Keltran

Reputation: 13

Is it possible to get the value of a type as a constant

Is it possible to do something like:

type TrueType = true;
const someVar = GetTypeValue<TrueType>(); // This is where the value true is written

Is it possible to write other constant values to constant variables like in C++?

Upvotes: 1

Views: 624

Answers (2)

cefn
cefn

Reputation: 3321

In the typescript world it's better to think of it the other way round if you need to use a constant as a runtime value. Define the constant, (so Javascript has it) then derive the type from it (so Typescript has it).

const GREAT_WORD = 'Discombobulate';
type GreatWord = typeof GREAT_WORD;


const SOUNDS_LIKE = 'Onomatopoeia'
const GOINGS_ON = 'Shenanigans'
const ALL_OVER = 'Ubiquitous'
const LESSER_WORDS = [SOUNDS_LIKE,GOINGS_ON, ALL_OVER];
type LesserWord = typeof LESSER_WORDS[number]

function say(word: GreatWord | LesserWord){
  console.log(word)
}


say(GREAT_WORD)
say(SOUNDS_LIKE)
say(GOINGS_ON)
say(ALL_OVER)

say('Discombobulate')
say('Shenanigans')

Upvotes: 1

Robert Rendell
Robert Rendell

Reputation: 2289

Typing helps at compile time but not at runtime.

You can use this strategy at compile time to get the value safely:

type TrueType = true;
const myTrue: TrueType = true;

Upvotes: 1

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