Typescript create dynamicaly union type from same interface props-CodePudding

I want to create union type from brother of same interface

like below


interface Foo {
  values: string[];
  defaultValue: string;
}

function fooo({values, defaultValue}: Foo) {}

fooo({values: ['a', 'b'], defaultValue: 'a'}); // this is correct example

fooo({values: ['a', 'b'], defaultValue: 'c'}); // I want to prevent this case!
// defaultValue must be 'a' or 'b'
// like tuple type 'a' | 'b'

Can I do this?

CodePudding user response：

Sure, you can achieve this by adding generic types.

interface Foo<K extends string[]> {
  values: [...K];
  defaultValue: K[number];
}

function fooo<K extends string[]>({values, defaultValue}: Foo<K>) {}

The generic type K will the tuple type of the value array. We then constrain defaultValue to only have the values specified in values with K[number].

Let's see if it works:

fooo({values: ['a', 'b'], defaultValue: 'a'});
fooo({values: ['a', 'b'], defaultValue: 'c'}); // error: Type '"c"' is not assignable to type '"a" | "b"'

Playground