TypeScript: How to write a function with conditional return type

Question

export type Name = { name: string }
export type Id = { id: number }
export type Value = T extends string ? Name : Id

export function create

        

Answer 1

Here is another solution which works great as well.

I like this solution better than the accepted answer because you will get correct type deduction when coding:

You can see when hovering, it correctly deduced the type.

Here is the code from the screenshot:

export type Name = { name: string }
export type Id = { id: number }
export type Value = T extends string ? Name : Id

export function create(value: T): Value {
    if (typeof value === 'string') return { name: value } as unknown as Value

    return { id: value } as unknown as Value
}