Tips for building an interface in TypeScript with a restricted range of indices

I'm working on a function that accepts parameters of type Record<string, string>. How can I define a type with a limited set of indexes without triggering a TypeScript compiler error?

Is there a way to create an interface with only specific index keys of a certain type?

type MyRecord = Record<string, string>

interface MyA {
    index1: string
    index2: 'true' | 'false'
}

function fn(a: MyRecord) {
    //perform operations
}

const myA: MyA = {
    index1: 'index',
    index2: 'true'
}
fn(myA) // throws error: Index signature is missing in type 'MyA'.

It seems like the solution involves changing MyA to be type My = {...}.

typescripttypescript-typings

Answer №1

If you want to incorporate an index signature into your type, one way to do it is like this:

interface MyA {
  property1: string
  property2: 'yes' | 'no'
  [key: string]: string;
}

It's important that the index signature align with your existing properties (in this example, string works well).

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