Typescript、typeof 等价于方法签名？

Question

很好奇是否有办法确定方法的签名。希望这段代码能说明这个问题：

class MyClass {
    constructor(public foo: any){}
}

const object1 = new MyClass((): void => {
    console.log('My function is to say hi. Hello!');
});
const object2 = new MyClass((n: number): void => {
    console.log('My function is echo a number. Here it is: ' + n);
});

object1.foo();      // My function is to say hi. Hello!
object2.foo(15);    // My function is echo a number. Here it is: 15

console.log(typeof object1.foo); // prints 'function'. 
                                 // I'm looking for something that prints '(): void' 
                                 // [or something comparable]

console.log(typeof object2.foo); // prints 'function'. 
                                 // I'm looking for something that prints '(number): void'

Answer 1

您需要考虑静态类型仅在设计时（TypeScript）可用，而不在运行时（JavaScript）可用：

class MyClass<T> {
    constructor(public foo: T){}
}

const sayHello = (): void => {
    console.log('My function is to say hi. Hello!');
};

const sayANumber = (n: number): void => {
    console.log('My function is echo a number. Here it is: ' + n);
};

const object1 = new MyClass(sayHello);

const object2 = new MyClass(sayANumber);

object1.foo();      // My function is to say hi. Hello!
object2.foo(15);    // My function is echo a number. Here it is: 15

// You can get the design-time types
type designtimeTypeOfFoo1 = typeof object1.foo; // () => void
type designtimeTypeOfFoo2 = typeof object2.foo; // (n: number) => number

// At run-time all the static type information is gone
const runtimeTypeOfFoo1 = typeof object1.foo; // "Function"
const runtimeTypeOfFoo2 = typeof object2.foo; // "Function"

// Error: design-time types are not available ar run-time
console.log(designtimeTypeOfFoo1, designtimeTypeOfFoo2);

// Success: run-time types are available at run-time
console.log(runtimeTypeOfFoo1, runtimeTypeOfFoo2);