function convert(x: P2): string;function convert(x: P1): number;function convert(x: P1 | P2): any { }const x1 = convert({ name: '' } as P1); // => numberconst x2 = convert({ name: '', age: 18 } as P2); // => string而我们只需要将函数重载列表的顺序调换一下，类型为 ...
interface Bird { fly(): void; layEggs(): void; } interface Fish { swim(): void; layEggs(): void; } declare function getSmallPet(): Fish | Bird; let pet = getSmallPet(); pet.layEggs(); // Only available in one of the two possible types pet.swim(); Property 'swim' does no...
AI代码解释 type Name=string;typeNameResolver=()=>string;type NameOrResolver=Name|NameResolver;functiongetName(n:NameOrResolver):Name{if(typeofn==='string'){returnn}else{reutrnn()}} 类型Name其实就是string的别名,类型() => string,一个函数返回一个字符串,这种格式就是类型NameResolver,NameOrReso...
json() as Promise<TodoWrong[]>; }); await getTodosWrong(); // !TypeError: Property '0/id' of the return value of 'function(): Promise<Array<{ userId: integer>0; id: string>0; title: string; completed: boolean }>>' must be a string (was number) ...
functionuseRef<T>(initialValue: T): MutableRefObject<T>;//convenience overload for refs given as a ref prop as they typically start with a null value/** * `useRef` returns a mutable ref object whose `.current` property is initialized to the passed argument ...
function doSomething(pair: readonly [string, number]) { pair[0] = "hello!"; } 在大多数代码中,元组往往被创建并不被修改,所以在可能的情况下,将类型注释为只读元组是一个很 好的默认。这一点也很重要,因为带有 const 断言的数组字面量将被推断为只读元组类型. let point = [3, 4] as const; fu...
function test<T extends string>(s: string, n: number, b: boolean, t: T) { let x1 = foo("*hello*"); // "hello" let x2 = foo("**hello**"); // "*hello*" let x3 = foo(`*${s}*` as const); // string let x4 = foo(`*${n}*` as const); // `${number}` ...
getOwnPropertySymbols(obj)) // 能取到 Symbol 和 name console.log(Reflect.ownKeys(obj)) // console.log(obj); 生成器 执行Generator函数会返回一个遍历器对象。 function* gen(){ yield Promise.resolve('小海') // 同步或者异步 yield '大海' yield '中海' yield '死海' } // 调用 执行 const ...
function test(a:number|undefined):string{if(a===undefined){return'';}return a.toString();}test();//TS2554:Expected1arguments,but got0. test(undefined); 1. 2. 3. 4. 5. 6. 7. 8. 之所以会报错是因为在 ts 中,undefined 是一个特殊的类型,由于类型为 undefined,并不代表可 缺省,因此示例...
functiongetUrls(url: string | URL, names: string[]){if(typeofurl==="string") {url=newURL(url); }returnnames.map(name => {url.searchParams.set("name", name)// ~~~// error!// Property 'searchParams' does not exist on type 'string | URL'.returnurl.toString(); }); } Here,...