typescript - Is it possible to restrict the type of a certain key to a certain value? - Stack Overflow

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In typescript,for an object,I can restrict its key to a specified range and value to a specified range. Can I restrict the type of a certain key to a certain value?

for example, I have this

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 I want to restrict when key = 'value1', the type of Value must be ValueType1, so as the value2. Is this possible?

In typescript,for an object,I can restrict its key to a specified range and value to a specified range. Can I restrict the type of a certain key to a certain value?

for example, I have this

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 I want to restrict when key = 'value1', the type of Value must be ValueType1, so as the value2. Is this possible?

• typescript
• syntactic-sugar

Share Improve this question Follow edited Nov 22, 2024 at 6:09 DarkBee 15.8k88 gold badges6969 silver badges110110 bronze badges asked Nov 22, 2024 at 3:55 Cody ZCody Z 2333 bronze badges 1

• 2 Uh, well you can define an interface that works that way, as shown in this playground link. But that's so obvious, I must be missing something. Presumably you are looking for something else, but what, exactly? Where does the information that value1 maps to ValueType1 and value2 maps to ValueType2 come from, if it's not hardcoded? (also: what does this question have to do with syntactic sugar?) – jcalz Commented Nov 22, 2024 at 3:58

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1 Answer 1

Sorted by: Reset to default 0

Just map the keys and types directly. Also I recommend using as const satisfies in the most cases since it will give you more precise/narrow types which could be a benefit later:

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

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