Typescript interface from array type

问题

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.

回答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 = {
  [key in SomeProperties[number]]: string;
}

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

Hope that helps; good luck!

回答2:

Worth noting: You can't iterate an tuple type in TypeScript

Actually, you can! Since TypeScript 3.1 you can safely use tuple types in mapped types like objects.

These sorts of operations can only be applied to types, not interfaces.

type SomeProperties = 'prop1' | 'prop2' | 'prop3';

type MyType = Record<SomeProperties, string>;

// equivalent to
// type MyType = {
//   [key in SomeProperties]: string
// }

Types and interface are the same from the perspective of the consumer (when you ask for a MyType, you don't care if it's an interface or a type, they're the same at that point)

来源：https://stackoverflow.com/questions/45607685/typescript-interface-from-array-type