typescript-conditional-types

Optional parameters based on conditional types

August 14, 2023 by Tarik

You can do this in 3.1 using Tuples in rest parameters and spread expressions const foo = <T extends string | number>( first: T, …a: (T extends string ? [boolean] : [undefined?]) ) => undefined; foo(‘foo’, true); // ok, as intended foo(2, true); // not ok, as intended foo(2, undefined); // ok, as intended foo(2); … Read more

Conditional types in TypeScript

February 15, 2023 by Tarik

One way to model this kind of logic is to use a union type, something like this interface Valid { isValid: true } interface Invalid { isValid: false errorText: string } type ValidationResult = Valid | Invalid const validate = (n: number): ValidationResult => { return n === 4 ? { isValid: true } : … Read more