Type narrow not worked with this union type.

[Mng12345]

🔎 Search Terms

type narrow

🕗 Version & Regression Information

TypeScript 5.8.3

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/HYQwtgpgzgDiDGEAEFgFcxSQbwFBIJQA8YB7AJwBcl5TgprUMkAlUgdwDEBLAG0ojkAKgE8YyPISlIAksHi80AE2hIAvEgCMAGnzSCAOVKU5C5ao0AmXfoIAhCJXYRU6pAGYbto5QdOXwG4ALF76dtwA5kIAFiCBGgCsodLhEQCCwEoAogCOaCC8MXFuAGzJUgAy0FBF8UgA7OWEVVBQGdl5BbVuABxNBLn5vG4AnP1IPoMFbpoADHoEAL64y7iUYshG5GAFPPyCouJuTJgAdGxcfALCG6dTwwA+KOhnF3vXhxCnk52PzxhQc4cd4HW6pbpPE6At5XUHiU4tGqxQKQl7Q4Gwm7w1Lte4Q-6vDH7LFfRG4361XBrDZITgUMBuSSENDcJQALiQDHI3GAEWSADNuBBeEoAKqsgD8HK5PL5CyQguJnw5Wx2vBBJOSADcCmgIBymfp1uIOQByQVECBKU3jHWKCBSpAvABGgiQTxlvNtuogyqQppdglN7v9noipvlixDhukxv1-sFwut40TIvFSkdYcjK2j8pZ7M5lG5XvlqbFkulRdlAsxfqhQMuSrBjmcrlRAIbGs+32MflbwGSvAg-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-LqRuCoHHue6JBGQXDkCCzlolIYTYNiLAYHIUhxCoIUsDepAgfk500GobhKG-J1jFOKlliAA

💻 Code

namespace enums {
    export const enum RowFilterType {
        Includes = 1,
        NotIncludes = 2,
        Between = 3,
        NotBetween = 4,
        BigThan = 5,
        BigAndEqualThan = 6,
        LessThan = 7,
        LessAndEqualThan = 8,
        Equal = 9,
        NotEqual = 10
    }
}

type NormalFilterType = enums.RowFilterType.Equal | enums.RowFilterType.NotEqual | enums.RowFilterType.BigThan | enums.RowFilterType.LessThan | enums.RowFilterType.BigAndEqualThan | enums.RowFilterType.LessAndEqualThan

type Form = {
    uid: string,
    fieldUid?: string,
    filterType: NormalFilterType,
    value: {
        type: 'fixed',
        value?: number | string,
        valueType: 'number' | 'string'
    } | {
        type: 'field',
        fieldUid?: string
    }
} | {
    uid: string,
    fieldUid?: string,
    filterType: enums.RowFilterType.Between | enums.RowFilterType.NotBetween,
    left?: number,
    right?: number
} | {
    uid: string,
    fieldUid?: string,
    filterType: enums.RowFilterType.Includes | enums.RowFilterType.NotIncludes,
    valueType: 'number' | 'string',
    value?: string
}

const required = {
    required: true,
    message: 'this field is required.'
}
const form = undefined as Form | undefined
let rules: Record<string, any>

if (form === undefined) {
    rules = {}
} else if (form.filterType === enums.RowFilterType.Between || form.filterType === enums.RowFilterType.NotBetween) {
    rules = {
        fieldUid: [required],
        left: [required],
        right: [required]
    }
} else if (form.filterType === enums.RowFilterType.Includes || form.filterType === enums.RowFilterType.NotIncludes) {
    rules = {
        fieldUid: [required],
        value: [required]
    }
} else {
    const filterType = form.filterType // typeof filterType is NormalFilterType
    const value = form.value // here the form should has properties of value, but it's not.

}

🙁 Actual behavior

See the line at 66, the type of form should be narrowed in this switch, but it's not.

🙂 Expected behavior

The type of form should be narrowed.

Additional information about the issue

No response

[MartinJohns]

I'll never understand why people don't try to minimize their demo and keep a lot of pointless noisy code. :-/

Regardless, this is a duplicate of #31404.

---

The simple workaround is to not have unions as discriminators:

type Form = {
    uid: string,
    fieldUid?: string,
    filterType: NormalFilterType,
    value: {
        type: 'fixed',
        value?: number | string,
        valueType: 'number' | 'string'
    } | {
        type: 'field',
        fieldUid?: string
    }
} | {
    uid: string,
    fieldUid?: string,
    filterType: enums.RowFilterType.Between,
    left?: number,
    right?: number
} | {
    uid: string,
    fieldUid?: string,
    filterType: enums.RowFilterType.NotBetween,
    left?: number,
    right?: number
} | {
    uid: string,
    fieldUid?: string,
    filterType: enums.RowFilterType.Includes,
    valueType: 'number' | 'string',
    value?: string
} | {
    uid: string,
    fieldUid?: string,
    filterType: enums.RowFilterType.NotIncludes,
    valueType: 'number' | 'string',
    value?: string
}

Or using a helper type using distributed conditional types to avoid the duplication:

type Unionize<K extends string, V, T> = V extends any ? ({ [P in K]: V } & T) : never

type Form = {
    uid: string,
    fieldUid?: string,
    filterType: NormalFilterType,
    value: {
        type: 'fixed',
        value?: number | string,
        valueType: 'number' | 'string'
    } | {
        type: 'field',
        fieldUid?: string
    }
} | Unionize<"filterType", enums.RowFilterType.Between | enums.RowFilterType.NotBetween, {
        uid: string,
        fieldUid?: string,
        left?: number,
        right?: number
    }
> | Unionize<"filterType", enums.RowFilterType.Includes | enums.RowFilterType.NotIncludes, {
        uid: string,
        fieldUid?: string,
        valueType: 'number' | 'string',
        value?: string
    }
>

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.