How to create a type for object based on enum structure

Question

I have a enum as below.

export enum Hotkey {
    MARK_IN = 'markIn',
    MARK_OUT = 'markOut',
    GO_TO_MARK_IN = 'goToMarkIn',
    GO_TO_MARK_OUT = 'goToMarkOut'
}

Now i want to create a type for a json object that should allow only the keys present in enum but not some random key during development.

type hotkey = keyof typeof Hotkey;

type clone = {[key:hotkey]: string}

const finalObject: clone = {
    MARK_IN : 'markIn'
};

i created the type as above but that is erroring out when i create the type "clone"

Error: An index signature parameter type cannot be a literal type or generic type. Consider using a mapped object type instead.ts(1337)

@KooiInc I know it's popular to keep reposting that, but it never sits right with me: a JSON object is an object that can be serialized to/from a JSON string. That definition is fairly intuitive and matches the way people use the term "JSON object" in the common parlance. — Jared Smith
– Jared Smith, Commented Dec 6, 2022 at 16:16

Brandon Taylor · Accepted Answer · 2022-12-06 15:59:26Z

1

You can create a type using an enum for the key this way:

export enum Hotkeys {
  MARK_IN = 'markIn',
  MARK_OUT = 'markOut',
  GO_TO_MARK_IN = 'goToMarkIn',
  GO_TO_MARK_OUT = 'goToMarkOut'
};

type IHotkey = `${ Hotkeys }`;

type IClone = {
  [key in IHotkey]?: string
};

If you want to use the enum member as the key you can also do:

const yourObject: IClone = {
  [Hotkeys.MARK_IN] = 'your-value'
}

edited Dec 6, 2022 at 15:59

answered Dec 6, 2022 at 15:29

Brandon Taylor

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2 Comments

Niranjan Over a year ago

Thanks for the answer Brandon. This was accepting the values in enum as key in my object. const finalObject: Iclone = { markIn : 'something' }; But i am expecting the other way round. like const finalObject: Iclone = { MARK_IN : 'markIn' };

Brandon Taylor Over a year ago

@Niranjan I've updated the answer with an example

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