How can I limit the keys in a Typescript object to only certain strings?

Question

How can I limit the keys in a Typescript object to only certain strings?

Is there a way in Typescript to create an object of type Partial with keys that can only be a combination of 'a', 'b', or 'c'? The object should not have all 3 keys, but it must have at least one. Here's what I've attempted so far:

// Defined keys:
type Keys = 'a' | 'b' | 'c'

// Desired object structure:
let partial: Partial = {'a': true}
let anotherPartial: Partial = {'b': true, 'c': false}

// Attempt using mapped types (does not work as intended):
type Partial = {
  [key in Keys]: boolean;
}

// Attempt using interfaces (also not achieving the desired result):
interface Partial = {
  [key: Keys]: boolean;
}

Neither of the methods I've tried seems to enforce the restriction I need. Can anyone provide a solution?

javascript string typescript object key

Answer 1

Answer №1

If you want to make the keys optional, you can simply use the ? symbol like this:

interface OptionalKeys {
   x?: boolean;
   y?: boolean;
   z?: boolean;
}

Alternatively, you can define it using the following syntax:

type Choices = "x" | "y" | "z";

type Selection = {
    [Choice in Choices]?: boolean
}

Answer 2

If you want to make the keys optional, you can simply use the ? symbol like this:

interface OptionalKeys {
   x?: boolean;
   y?: boolean;
   z?: boolean;
}

Alternatively, you can define it using the following syntax:

type Choices = "x" | "y" | "z";

type Selection = {
    [Choice in Choices]?: boolean
}

Answer 3

Answer №2

Here is an alternative method...

// Defining a type for keys
type Keys = 'a' | 'b' | 'c'

// Creating a type that includes all keys
type WithAllKeys = {
  [key in Keys]: boolean;
}

// Creating an interface with Partial keys
interface WithPartialKeys: Partial<WithAllKeys>;

Answer 4

Here is an alternative method...

// Defining a type for keys
type Keys = 'a' | 'b' | 'c'

// Creating a type that includes all keys
type WithAllKeys = {
  [key in Keys]: boolean;
}

// Creating an interface with Partial keys
interface WithPartialKeys: Partial<WithAllKeys>;

How can I limit the keys in a Typescript object to only certain strings?

Answer №1

Answer №2

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