小编IAm*_*ber的帖子

考虑到下面的类型、接口和 getData 函数，我试图找到一种利用可区分联合的方法，以便 TS 编译器可以将返回类型缩小getData(source: DOSources)为关联的DOTypes

// Expected behavior
const result = getData("dataObjectA");

// result.data should be a string but in this case the TS compiler will complain 
// that data does not have the toLowerCase() function
result.data.toLowerCase();

示例代码

interface DataObjectA {
  source: "dataObjectA";
  data: string;
}

interface DataObjectB {
  source: "dataObjectB";
  data: number;
}


type DOTypes = DataObjectA | DataObjectB
type DOSources = DOTypes["source"];

async function getData(source: DOSources) {
  const response = await fetch(`https://some-random-endpoint/`, {
    method: …