泛型获取类名

Question

I have a generic function that I would like to get the name of the class that is passed in.

public addComponent<T extends Component>(): Component {
    comp = new Component() as T;
    comp.name = T.constructor.name;
    console.log(comp.name);
    return comp;
}

Then lets say I call it like so:

obj.addComponent<MyClass>();

I would then expect the log to display "MyClass". But currently I get an error saying:

Cannot find name 'T'.

Answer 1

There's no way to do that.

The T doesn't exist at runtime, it's only for compilation and the compiler removes that (along with the types) so the resulting javascript for this:

class MyFactory {
    public addComponent<T extends Component>(): Component {
        let comp = new Component() as T;
        comp.name = T.constructor.name;
        console.log(comp.name);
        return comp;
    }
}

Is:

var MyFactory = (function () {
    function MyClass() {
    }
    MyFactory.prototype.addComponent = function () {
        var comp = new Component();
        comp.name = T.constructor.name;
        console.log(comp.name);
        return comp;
    };
    return MyFactory;
}());

As you can see, the js code doesn't have the generics signature, so there's no definition for T , and so T.constructor results in the error you're receiving.

If you want the method to create an instance of a class by passing it then it should look like:

interface ComponentConstructor<T extends Component> {
    new(): T;
    name: string;
}

class Component {
    name: string;
}

class MyComponent extends Component {}

class MyFactory {
    public addComponent<T extends Component>(ctor: ComponentConstructor<T>): Component {
        let comp = new ctor();
        comp.name = ctor.name;
        console.log(comp.name);
        return comp;
    }
}

let factory = new MyFactory();
let obj = factory.addComponent(MyComponent as ComponentConstructor<MyComponent>);

( code in playground )