Problem extending native (es6) classes in Safari

Question

I'm having trouble extending the native WebSocket class using es6 classes.

The following piece of code works on Chrome and Firefox, but not on Safari:

class MyWebSocket extends WebSocket {
    doSomething() {
        console.log('hi');
    }
}

let ws = new MyWebSocket('wss://127.0.0.1:4000');
ws.doSomething();

TypeError: ws.doSomething is not a function. (In 'ws.doSomething()', 'ws.doSomething' is undefined)

console.log('MyWebSocket.prototype') lets me see that the function was added to the prototype. This happens with a few other builtin classes, Animation being one, but not with others, like Date for example.

Has anyone run into this? Is this a bug in Safari? Any advice is appreciated!

Answer 1

Yes, looks like a bug. The WebSocket constructor is probably hardcoded to return a WebSocket instance. It doesn't respect Symbol.species either.

As a workaround you could use something like this:

class MyWebSocket extends WebSocket {
    constructor(url) {
        super(url);
        Object.setPrototypeOf(this, MyWebSocket.prototype);
    }