Typescript interface from array type

Question

I need to force an array to have a specific set of values that should be then the keys of my interface. I can force the array with

type SomeProperties = ['prop1', 'prop2', 'prop3'];

but I don't know how to force an interface to have those properties. I tried something like

type MyInterface = {
  [key in keyof SomeProperties]: string;
}

but obviously the keys of an array are just numbers so my interface become

interface MyInterface {
  0: string;
  1: string;
  2: string;
}

instead of the wanted interface

interface MyInterface {
  prop1: string;
  prop2: string;
  prop3: string;
}

Do you know if there is a way to achieve this in Typescript?

It would be useful because I need to iterate on some properties to "clone" an object and I also need to access to those properties easily. Repeating the properties in both type and interface is a bit fragile for me.

Answer 1

As you note, the strings you're trying to access aren't the keys of SomeProperties, but the elements of SomeProperties.

You can use the indexed access operator here: if K is a key (or a union of keys) of T, then T[K] is the property type (or union of property types) corresponding to accessing the K key(s) of T.

Tuples and arrays accept number as a key type, so you want to use SomeProperties[number] to give you the union "prop1"|"prop2"|"prop3":

type SomeProperties = ['prop1', 'prop2', 'prop3'];

type MyInterface = {
  [K in SomeProperties[number]]: string;
}

const myInterface: MyInterface = {
  prop1: 'this',
  prop2: 'works',
  prop3: 'now'
}

Playground link to code