typescript omit remove unwanted properties-CodePudding

I havve the following types:

type A = {
    role: 'admin',
    force?: boolean
}

type B = {
    role: 'regular'
}

type Req = { data: number } & (A | B);

When when I do some manipulation on Req force is removed for some reason:

type NoData = Omit<Req, 'data'>;

const noData: NoData = {
    role: 'admin',
    force: true
}

and I get:

Type '{ role: "admin"; force: boolean; }' is not assignable to type 'NoData'.
  Object literal may only specify known properties, and 'force' does not exist in type 'NoData'.(2322)

TypeScript Playground

CodePudding user response：

The default version ofOmit is not distributive, meaning it will apply to the union as a whole, or more specific to the common properties of the union, rather than to each constituent of the union

You can create a distributive version using distributive conditional types :

type A = {
    role: 'admin',
    force?: boolean
}

type B = {
    role: 'regular'
}

type Or = { data: number } & (A | B);
type DistributiveOmit<T, K extends PropertyKey> = T extends T ? Omit<T, K> : never;
type NoData = DistributiveOmit<Or, 'data'>;

const noData: NoData = {
    role: 'admin',
    force: true
}

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