Map typescript interface to related interface

Question

Say I have a typescript interface:

interface IOriginal {
    aaa: string;
    bbb: boolean;
}

... and now say that I want to create a similar interface with identical keys but different values (in my specific case the values are derived using the Reducer generic from Redux, but I'd like to keep the answer quite general):

import { Reducer } from "redux";
interface IDerived{
    aaa: Reducer<string>;
    bbb: Reducer<boolean>;
}

Question: how can I generate IDerived directly from IOriginal without explicitly retyping all the key-value pairs (violating DRY and having two places to update stuff)? If these were objects I could do sth like this:

const derived = original;
for(var key in derived) derived[key] = Reducer(original[key]);

... but I'm not sure if there are equivalent tools when dealing with types/interfaces.

Matt McCutchen · Accepted Answer · 2018-07-29 23:09:27Z

4

You're looking for a mapped type:

type IDerived = { [K in keyof IOriginal]: Reducer<IOriginal[K]> };

answered Jul 29, 2018 at 23:09

Matt McCutchen

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