根据TypeScript中的参数值更改返回类型

Question

我有以下功能:

function doThing(shouldReturnObject: boolean): string | object {
    return shouldReturnObject ? { hello: 'world' } : 'hello world';
}

我希望返回值在shouldReturnObjectequals为true 时为对象,但在为false时为字符串.

Answer 1

免责声明:在大多数情况下,这不被视为最佳做法.如果你想这样做,你应该重新考虑你的架构.

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解决方案是重载函数.为每个参数值重载函数并更新返回类型,如下所示:

doThing(shouldReturnObject: true):  object
doThing(shouldReturnObject: false): string
doThing(shouldReturnObject: boolean): string | object {
  return shouldReturnObject ? { hello: 'world' } : 'hello world';
}

如果参数是对象,也可以实现这一点.例如:

interface DoThingsSettings {
  lazyLoading: boolean;
}

doThing(settings: { lazyLoading: false} &  DoThingsSettings): object[]
doThing(settings: { lazyLoading: true} &  DoThingsSettings): string[]
doThing(settings: DoThingsSettings):  object[] |  string[] {
  return settings.lazyLoading ? [{ name: 'Peter' }] : ['/user/1'];
}