问题描述
exampleFunction = (param: string) => {
try {
const result = processstring(param) as { resultExample: string };
return { isSuccess: true,...result };
catch (error) {
return { isSuccess: false };
}
}
理想情况下,返回值的类型为:{ isSuccess: true,resultExample: string} | { isSuccess: false }
,但其类型为{ isSuccess: boolean,resultExample: string } | { isSuccess: boolean }
,这令人沮丧,因为这意味着我无法利用类型保护。
const data = exampleFunction("exampleParam");
if (data.isSuccess) {
functionExpectingResultExample(data.resultExample); // Type Error because "resultExample: string | {}" is not assignable to "resultExample: string"
}
以上内容不应出错,因为应将true和false用作类型保护,而应将它们键入为布尔值。
我唯一的手动输入为true和false的解决方案吗?
解决方法
您需要将isSuccess
返回类型强制转换为const
,以便TypeScript知道该值不是布尔值,而是特定的,不变的布尔值:
const exampleFunction = (param: string) => {
try {
const result = processString(param) as { resultExample: string };
return { isSuccess: true as const,...result };
} catch (error) {
return { isSuccess: false as const };
}
}
签出proof-of-concept on TypeScript Playground。
如果愿意,还可以将整个返回的对象强制转换为const。
const exampleFunction = (param: string) => {
try {
const result = processString(param) as { resultExample: string };
return { isSuccess: true,...result } as const;
} catch (error) {
return { isSuccess: false } as const;
}
}