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); // => st
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...
log("This is my warning message"); } => tsc => function warnUser() { console.log("This is my warning message"); } 需要注意的是,声明一个 void 类型的变量没有什么作用,因为它的值只能为 undefined 或null: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 let unusable: void = undefined...
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) ...
startsWith("class")) { return new (comp as new () => Component)(); } let res: any; try { // 当成函数来调用,看看结果是什么 res = (comp as Function)(); } catch (e) { // 在 es6 中,构造器必须使用 new ,直接调用会报错: // Class constructor A cannot be invoked without 'new'...
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 getUrls(url: string | URL, names: string[]) { if (typeof url === "string") { url = new URL(url); } return names.map(name => { url.searchParams.set("name", name) // ~~~ // error! // Property 'searchParams' does not exist on type 'string | URL'. return url....
最简单描述一个函数的方式是使用函数类型表达式(function type expression)。它的写法有点类似于箭头函数: function greeter(fn: (a: string) => void) { fn("Hello, World"); } function printToConsole(s: string) { console.log(s); } greeter(printToConsole); ...
When deploying your function, specify index.handler for the Handler property. The value of the Handler property is the file name and the name of the exported handler method, separated by a dot. uploadReceiptToS3 function: This is a helper function that's referenced by the main handler ...
functionstart(pet: Bird | Fish){// 调用 layEggs 没问题,因为 Bird 或者 Fish 都有 layEggs 方法pet.layEggs(); // 会报错:Property 'fly' does not exist on type 'Bird | Fish'// pet.fly(); // 会报错:Property 'swim' does not exist on type 'Bird ...