Typescript generic base class that defines a base callback type

Question

I am trying to create a generic base event class:

class BaseEvent<T extends { (args?: any[]): void }> {
    addEventListener(listener: T): { (): void } {
        return () => { };
    }
}

That I can extend to specify the restrict the parameters of the callback:

class ExtraSpecialEvent
    extends BaseEvent<{ (foo: string): void }> {

}

But I cant seem to figure out the syntax. Here is a playground demonstrating my problem.

Any idea how to accomplish this?

---- UPDATE ----

As answered below by @murat-k, my generic is asking for an array... While this is what my question asks, its not what I meant. My intention was to allow 0 or more any args. The solution to my problem was to change the generic to:

class BaseEvent<T extends { (...args: any[]): void }> {
    addEventListener(listener: T): { (): void } {
        return () => { };
    }
}

Murat Karagöz · Accepted Answer · 2017-02-17 15:50:04Z

1

You are declaring args as an array type. You have to pass it as a array e.g.

class ExtraSpecialEvent
    extends BaseEvent<{ (foo: string[]): void }> {

}

answered Feb 17, 2017 at 15:50

Murat Karagöz

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2 Comments

Lucas Over a year ago

Ok, yes, you are correct. I will mark this as the answer... Though it turns out I was asking the question wrong... I really wanted the ability to specify 0 or more any args... This answer sent me down the right path.

Murat Karagöz Over a year ago

@Lucas For that you could use the ... rest parameter. See here for an example stackoverflow.com/questions/12697275/…

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