通常我喜欢在扩展对象类型时使用交叉类型。

type FieldKey = 'internal' | 'external'

type ValidateResult = {
  [x in FieldKey]: any;
} & {
  newKey: any;
}
// type ValidateResult = {
//     internal: any;
//     external: any;
//     newKey: any;
// }

TypeScriptPlayground
但是，如果对象中的所有属性都具有相同的值类型，则可以在Mapped Type中使用新的Union Type，如下所示：

type FieldKey = 'internal' | 'external'

type ValidateResult = {
  [x in FieldKey | "newKey"]: any;
}
// type ValidateResult = {
//     internal: any;
//     external: any;
//     newKey: any;
// }

TypeScriptPlayground

为什么不添加一个新的类型定义，并带有缺少的键，就像这样：

type FieldKey = 'internal' | 'external'
type ValidateResultKey = FieldKey | 'you_done_goofed'

export type ValidateResult = {
  [x in ValidateResultKey]: any
}

或者，如果需要另一种类型，可以使用&运算符并将其与另一种类型合并组合

type FieldKey = 'internal' | 'external'

export type ValidateResult = {
  [x in FieldKey]: any;
} & {
  test: string;
}

const test = {
  internal: "",
  external: "",
  test: "",
} as ValidateResult;

如果你想更通用，你可以扩展基类型：

type FieldKey = 'internal' | 'external'

type ValidateResult<T extends (string | undefined) = undefined> = {
  [x in (FieldKey | T) as x extends undefined ? never : x]: any;
}

// Now you can define your custom types:

type ValidateResultWithNewField= ValidateResult<'newField'>;

// or event

type ValidateResultWithMultiNewFields = ValidateResult<'field1' | 'f2' | 'anotherField' | 'etcField'>;