此TypeScript语法是什么意思？

Question

I am watching a video about RxJS and have come across some TypeScript syntax I've not seen before. It doesn't matter that it's RxJS, it's a generic question, but I thought I'd just add that it was RxJS.

It's the call to super() in this that I don't understand:

class MyObservable extends Rx.Observable {
    constructor(initialValue) {
        super(observer) => {
            observer.next(initialValue);
            this.observer = observer;
        }
    }
}

The video goes on to point out that this is not a good way to extend observable functionality, but that's not what I'm interested in anyway. I'm interested in the call to super() : what's going on here? The best that I can come up with is that it is shadowing the base class's constructor, but I'm not sure. Can anyone elucidate?

Answer 1

This is definitely a typo. The constructor for Rx.Observable takes a function argument, which itself takes a Subscriber - an object with 'next' (as confirmed by your code), and 'error'/'complete' methods, although those aren't used in the code above. This was almost certainly meant to be

class MyObservable extends Rx.Observable {
    constructor(initialValue) {
        super((observer) => {
            observer.next(initialValue);
            this.observer = observer;
        });
    }
}

This also makes sense from what the video is describing, about extending Rx functionality - you're effectively 'capturing' the observer and passing it an additional initial value, before setting it to this.observer and letting Rx.Observable continue to do its thing.