Question

我正在尝试将Union类型用于React组件的道具

type Props =
  | {
      type: "string"
      value: string
    }
  | {
      type: "number"
      value: number
    }
  | {
      type: "none"
    }

class DynamicProps extends React.Component<Props> {
  render() {
    return null
  }
}

// Ok
const string_jsx = <DynamicProps type="string" value="hello" />

// Error as expected, value should be a string
const string_jsx_bad = <DynamicProps type="string" value={5} />

// Ok
const number_jsx = <DynamicProps type="number" value={5} />

// Error as expcted value should be a number
const number_jsx_bad = <DynamicProps type="number" value="hello" />

// Error as expected, invalid isn't a property on any of the unioned types
const extra = <DynamicProps type="string" value="extra" invalid="what" />

// No error? There should be no value when type="none"
const none_jsx = <DynamicProps type="none" value="This should be an error?" />

// Ok, seems like value has become optional
const none2_jsx = <DynamicProps type="none" />

// Error as expected, value is not present. Value doesn't seem to be made optional all the time
const required = <DynamicProps type="string" />

似乎有效的道具会根据type道具的不同而部分起作用。但是，虽然没有出现在联合中的任何类型上的额外属性将是一个错误，但似乎出现在至少一个联合类型中但不基于判别属性的类型将不是错误。

我不确定为什么会这样。将联合类型用作反应组件的支撑是一种反模式吗？

Answer 1

涉及工会时，问题与多余的财产检查有关。您可以阅读关于类似问题的答案here。其要点是，多余的联合检查属性允许对象上存在任何成员的任何键。我们可以通过引入额外的类型的成员来避免这种情况，即永远不要确保具有过多属性的对象与特定成员不会错误兼容：

type Props =
| {
    type: "string"
    value: string
    }
| {
    type: "number"
    value: number
    }
| {
    type: "none"
    }

type UnionKeys<T> = T extends any ? keyof T : never;
type StrictUnionHelper<T, TAll> = T extends any ? T & Partial<Record<Exclude<UnionKeys<TAll>, keyof T>, never>> : never;
type StrictUnion<T> = StrictUnionHelper<T, T>

class DynamicProps extends React.Component<StrictUnion<Props>> {
    render() {
        return null
    }
}
// error now
const none_jsx = <DynamicProps type="none" value="This should be an error?" />

Typescript React：提供多余属性时，道具的并集类型不会显示错误

1 个答案: