How to define an index signature in Typescript that includes both mandatory and optional keys

I am on a quest to discover a more refined approach for creating a type that permits certain keys of its index signature to be optional.

Perhaps this is a scenario where generics would shine, but I have yet to unlock the solution.

At present, my construction method looks like this:

// Define required and optional keys allowed as indexes in the final type
type RequiredKeys = 'name' | 'age' | 'city'
type OptionalKeys = 'food' | 'drink'

// Create index types to combine into the final type
type WithRequiredSignature = {
    [key in RequiredKeys]: string
}
type WithOptionalSignature = {
    [key in OptionalKeys]?: string
}

// Construct the type with both required and optional properties in the index signature
type FinalType = WithRequiredSignature & WithOptionalSignature

// Test objects with autocomplete functionality
const test1: FinalType = {
    name: 'Test',
    age: '34',
    city: 'New York'
}

const test2: FinalType = {
    name: 'Test',
    age: '34',
    city: 'New York',
    drink: 'Beer'
}

const test3: FinalType = {
    name: 'Test',
    age: '34',
    city: 'New York',
    food: 'Pizza'
}

Answer №1

Using an interface can be a great solution if you are not receiving the keys dynamically. It provides a structured way to define the properties of an object.

interface Person {
   name: string;
   age: number;
   city: string;
   food?: string;
   drink?: string;
}

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