TypeScript：检查派生类是否实现方法

Question

I got two classes, one deriving from the other, and on the base class I need to check if the derived class is implementing a method with a specific name:

class Foo {
    constructor() { }

    childHasMethod() {
        if(this.method) {
            console.log('Yay');
        } else {
            console.log('Nay');
        }
    }
}

class Bar extends Foo {
    constructor() {
        super();
        this.childHasMethod();
    }

    method() {

    }
}

var bar = new Bar();

Even though the line if(this.method) { is marked red on the playground, it works. But the local compiler throws a compilation error: The property 'method' does not exist on value of type 'Foo' .

Is there a clean way to achieve what I'm trying to do?

Answer 1

In order to "sneak it past the compiler" you can treat this as dynamic:

(<any>this).method

I have made a full example of this on the TypeScript Playground .

childHasMethod() {
    if((<any>this).method) {
        alert('Yay');
    } else {
        alert('Nay');
    }
}

Having said this, having a base class know details about its sub-classes could get you into tricky places. Usually I would try to avoid this as it sounds like the specialisations are leaking into the base class - but you may have a particular thing you are doing and know your program better than me so I'm not saying "don't do this" - just "are you sure" :)