CODEWITHSUNDEEP
typescript
Anel Drocic
Anel Drocic

Reputation: 69

In TypeScript, is there a way to omit a type of true or false?

This was my best attempt at trying this. Is it possible or even necessary? Maybe there is something I'm missing about typescript that makes more sense.

const TrueOrFalse = True | False;

const OnlyTrue = Omit<TrueOrFalse, false>;

Upvotes: 1

Views: 1058

Answers (1)

Titian Cernicova-Dragomir
Titian Cernicova-Dragomir

Reputation: 249686

Omit removes properties from an object type. What you want to do is exclude a type from a union. You can do this with the built-in conditional type Exclude. 

type X = Exclude<boolean, true> // X is false

Playground Link

Exclude will take out of the first type parameter, any type that is a subtype of the second parameter.

You can read more about exclude here

Exclude and its cousin Extract can be useful also in manipulating discriminated unions, to extract or exclude a specific constituent from a union, even if you only know the discriminant not the whole the type:

type Shape = { type: "sq", size: number } | { type: "circle", radius: number }


type Square = Exclude<Shape, { type: "circle" }> //  { type: "sq", size: number }
type Circle = Extract<Shape, { type: "circle" }> //  { type: "circle", radius: number }

Playground Link

Upvotes: 4

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