Typescript interface keys from enum different types

Question

I have list of properties that should be as a keys of interfaces with different types. How better to implement them? I want not to allowed to use properties that not exist in enum.

export enum SomePropetries {
  prop1,
  prop2,
  prop3
};

export interface PropsInterface {
  [SomePropetries.prop1]: number;
  [SomePropetries.prop2]: boolean;
  [SomePropetries.prop3]: string;
}


// Usage example. 
// I have object of properties. Each of property can be updated separatelly.

let props: PropsInterface = {
   [SomePropetries.prop1]: null,
   [SomePropetries.prop2]: null,
   [SomePropetries.prop3]: null
};

const fieldToUpdate: {
  field: SomePropetries;
   value: number;
} = {
   field: SomePropetries.prop1,
   value: 123
};

props[fieldToUpdate.field] = fieldToUpdate.value;

please provide reproducible example, your exmaples contains a syntax errors — captain-yossarian from Ukraine
– captain-yossarian from Ukraine, Commented Oct 19, 2021 at 12:07
let fieldToUpdate { and field: Properties = Properties.prop1, is not valid syntax — captain-yossarian from Ukraine
– captain-yossarian from Ukraine, Commented Oct 19, 2021 at 13:36
Now I fixed a lot. Please check. I only have a n error: Type 'number' is not assignable to type 'never'. But this is my problem — Sergey Kudryashov
– Sergey Kudryashov, Commented Oct 19, 2021 at 13:38

captain-yossarian from Ukraine · Accepted Answer · 2021-10-19 13:44:35Z

1

First of all, you need to make PropsInterface all properties nullable.

export enum SomePropetries {
  prop1,
  prop2,
  prop3
};

interface PropsBase {
  [SomePropetries.prop1]: number;
  [SomePropetries.prop2]: boolean;
  [SomePropetries.prop3]: string;
}

type NullableRecord<T> = {
  [Prop in keyof T]: T[Prop] | null
}

type PropsInterface = NullableRecord<PropsBase>

Then, you are allowed to use null as a property type.

let props: PropsInterface = {
  [SomePropetries.prop1]: null,
  [SomePropetries.prop2]: null,
  [SomePropetries.prop3]: null
}

This does not work,

const fieldToUpdate = {
  field: SomePropetries.prop1,
  value: 123
}

props[fieldToUpdate.field] = fieldToUpdate.value;

because fieldToUpdate.field is infered as enum. I mean it expect all possible enum keys, whereas you are interested in only one SomePropetries.prop1.

Hence, in order to make it work, you should just use as const assertion.

const fieldToUpdate = {
  field: SomePropetries.prop1,
  value: 123
} as const

props[fieldToUpdate.field] = fieldToUpdate.value;

Whole code:

export enum SomePropetries {
  prop1,
  prop2,
  prop3
};

interface PropsBase {
  [SomePropetries.prop1]: number;
  [SomePropetries.prop2]: boolean;
  [SomePropetries.prop3]: string;
}

type NullableRecord<T> = {
  [Prop in keyof T]: T[Prop] | null
}

type PropsInterface = NullableRecord<PropsBase>


// Usage exanple. 
// I have object of properties. Each of property can be updated separatelly.

let props: PropsInterface = {
  [SomePropetries.prop1]: null,
  [SomePropetries.prop2]: null,
  [SomePropetries.prop3]: null
};

const fieldToUpdate = {
  field: SomePropetries.prop1,
  value: 123
} as const

props[fieldToUpdate.field] = fieldToUpdate.value;

Playground

edited Oct 19, 2021 at 13:44

answered Oct 19, 2021 at 11:44

captain-yossarian from Ukraine

33.5k5 gold badges41 silver badges78 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Sergey Kudryashov Over a year ago

Thank you! But how to make exact types?

captain-yossarian from Ukraine Over a year ago

What do you mean exact? Could you please provide an example?

Sergey Kudryashov Over a year ago

I edited my example. Please have a look.

Sergey Kudryashov Over a year ago

Now works good! Thank you so much. Here is some magic with nullableRecord. I have to learn about it ))

Collectives™ on Stack Overflow

Typescript interface keys from enum different types

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related