Turn TypeScript - Modify type properties to reflect types of their descendants

I am currently working on creating a type that will modify a generic type based on its children. To provide some clarity, I have created a simplified example below:

Original type

type FormFields = {
        username: {
            type: string,
            name: 'User Name'
        },
        password: {
            type: string,
            name: 'Password (must be strong)'
        };
    }
    

I want to transform it so that it can be utilized as

const userInput: UserInput<FormFields> = ...;
    

where the type of userInput would essentially be

{username: string, password: string}
    

Ideally, I attempted something like this, but encountered an error:

type UserInput<T> = {
        [K in keyof T]: T[K]['type'];
    }
    

Any assistance or guidance in the right direction would be highly appreciated!

Answer №1

Almost there! Just remember to add a constraint on T so that TS can recognize that all members of T will have the necessary type property:

type UserInput<T extends Record<string, { type: string}>> = {
    [K in keyof T]: T[K]['type'];
}

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