Use an Enum as Restricted Key or Value type in TypeScript

# Use an Enum as Restricted Key or Value type in TypeScript

Use keyof typeof to use an enum as a restricted keys type.

The constructed type will contain all of the enum keys with their values being initialized to any.

index.ts

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enum Sizes {
  Small = 'S',
  Medium = 'M',
  Large = 'L',
  ExtraLarge = 'XL',
}

/**
 * 👇️ let values: {S: any; M: any; L: any; XL: any}
 */
let values: { [key in Sizes]: any };

/**
 * 👇️ let keys: {Small: any; Medium: any; Large: any; ExtraLarge: any}
 */
let keys: { [key in keyof typeof Sizes]: any };

use enum as restricted key or value type

The code for this article is available on GitHub

The first example shows how to construct a type that includes the enum values as keys and the second constructs a type using the enum keys.

If you don't want to have all the keys or values in the constructed type be required, set them to optional by using a question mark.

index.ts

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enum Sizes {
  Small = 'S',
  Medium = 'M',
  Large = 'L',
  ExtraLarge = 'XL',
}

/**
 * 👇️ let values: {S?: any; M?: any; L?: any; XL?: any}
 */
let values: { [key in Sizes]?: any };

/**
 * 👇️ let keys: {Small?: any; Medium?: any; Large?: any; ExtraLarge?: any}
 */
let keys: { [key in keyof typeof Sizes]?: any };

Now the consumer can only specify the keys they need.

index.ts

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enum Sizes {
  Small = 'S',
  Medium = 'M',
  Large = 'L',
  ExtraLarge = 'XL',
}

/**
 * 👇️ let values: {S?: any; M?: any; L?: any; XL?: any}
 */
let values: { [key in Sizes]?: any };

values = { M: 'medium' };

/**
 * 👇️ let keys: {Small?: any; Medium?: any; Large?: any; ExtraLarge?: any}
 */
let keys: { [key in keyof typeof Sizes]?: any };

keys = { Large: 'large' };

The code for this article is available on GitHub

When working with enums, keyof typeof constructs a type that represents all enum keys as strings.

index.ts

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enum Sizes {
  Small = 'S',
  Medium = 'M',
  Large = 'L',
  ExtraLarge = 'XL',
}

// 👇️ type KeysUnion = "Small" | "Medium" | "Large" | "Extra Large"
type KeysUnion = keyof typeof Sizes;

If you need to check if a value exists in an enum, click on the following article.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

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Use an Enum as Restricted Key or Value type in TypeScript

# Use an Enum as Restricted Key or Value type in TypeScript

# Additional Resources

Borislav Hadzhiev