同样，在TypeScript 中也支持这样的参数类型定义，如下代码所示：function sum(...nums: number[]) {return nums.reduce((a, b) => a + b, 0);}sum(1, 2); // => 3sum(1, 2, 3); // => 6sum(1, '2'); // ts(2345) Argument of type 'string' is not assignable to parameter of ...
As mentioned before, this is a required part of the function type, so if the function doesn’t return a value, you would use void instead of leaving it off. 代码语言:javascript 代码运行次数:0 运行 AI代码解释 let myAdd: (x: number, y: number) => number = function ( x: number, y...
// !TypeError: The 1st argument of 'function range(integer>=0): Array<(integer>=0)>' (overload 1 of 2) must be an integer (was 0.5) 不妨在 StackBlitz 上在线体验下。 这个range 函数的类型被自动推导为 Safunc<((n: number) => number[]) & ((n1: number, n2: number, n3?: ...
log(arg.length); return arg; } loggingIdentity(7); // index.ts(10,17): error TS2345: Argument of type '7' is not assignable to parameter of type 'Lengthwise'. 多个类型参数之间也可以互相约束: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 function copyFields<T extends U, U>(...
enumA{x='x',y='y',z='z',}enumB{x='x',y='y',z='z',}function fn(val:A){}fn(B.x);//TS2345:Argument of type'B.x'isnotassignable to parameter of type'A'.; 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
function toNumber(input: unknown): number { return input as number; } const foo = toNumber('123'); foo的ts类型是number,但它的js类型是string。真的要转number,应该这么写: function toNumber(input: unknown): number { return Number(input); } 慎用类型断言 考虑下面这段代码: interface Foo ...
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 arrayAsString<T>(names:T[]): string { return names.join(", ");}泛型将允许这些类型的实用函数变得类型安全,从而避免过程中使用any类型。 类的扩展 我们已经看到泛型约束与Reaction类组件一起用来约束属性和状态,但它们也可以用来确保类属性被正确的格式化。以下面的示例为例,确保在函数需要时同时定义...
function sum(x: number, y: number): number { return x + y; } 1. 2. 3. 函数表达式 let mySum: (x: number, y: number) => number = function (x: number, y: number): number { return x + y; }; 1. 2. 3. 注意: 在TypeScript的类型定义中,=>用来表示函数的定义,左边是输入类型...
functionisFish(fish: Bird | Fish):boolean{return!!(fishasFish).swim;} functionstart(pet: Bird | Fish){// 调用 layEggs 没问题,因为 Bird 或者 Fish 都有 layEggs 方法pet.layEggs(); if(isBird(pet)) {(petasBird).fly();}elseif(isFish(pet)) {(peta...