Can we limit a specific key to only accept a specific value?

Question

Can we limit a specific key to only accept a specific value?

Is it possible to restrict the type of a certain key to a certain value in TypeScript for an object?

For instance, consider the following example:


interface ValueType1 {
    key1: string,
    key2: string,
}

interface ValueType2 {
    key3: number,
    key4: number,
}

type KeyType = 'value1' | 'value2';

const map: {[key in KeyType]: ValueType1 | ValueType2} = {
    'value1': {
        key1: '123',
        key2: '123'
    },
    'value2': {
        key3: 123,
        key4: 123,
    }
}

If we want to ensure that when key = 'value1', the type of Value must be ValueType1 and similarly for value2, is this achievable?

typescript syntactic-sugar

Answer 1

Answer №1

Simply pair the keys with their corresponding types directly. I also suggest utilizing as const satisfies in most scenarios as it can provide more precise and narrow types, which may be advantageous later on:

Playground

type ValueMap = {
  value1: ValueType1,
  value2: ValueType2
}

const map: ValueMap = {
    'value1': {
        key1: '123',
        key2: '123'
    },
    'value2': {
        key3: 123,
        key4: 123,
    }
}

const constMap = {
    'value1': {
        key1: '123',
        key2: '123'
    },
    'value2': {
        key3: 123,
        key4: 123,
    }
} as const satisfies ValueMap

Answer 2

Simply pair the keys with their corresponding types directly. I also suggest utilizing as const satisfies in most scenarios as it can provide more precise and narrow types, which may be advantageous later on:

Playground

type ValueMap = {
  value1: ValueType1,
  value2: ValueType2
}

const map: ValueMap = {
    'value1': {
        key1: '123',
        key2: '123'
    },
    'value2': {
        key3: 123,
        key4: 123,
    }
}

const constMap = {
    'value1': {
        key1: '123',
        key2: '123'
    },
    'value2': {
        key3: 123,
        key4: 123,
    }
} as const satisfies ValueMap

Can we limit a specific key to only accept a specific value?

Answer №1

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