How to use "ws.once" with this library?

Hello!

I adopted this package when I was needing to have my WS connections restarted if they disconnect. It worked perfectly in my case, since I was using this to follow up crypto-currencies value changes.

Now I wish to also have a channel open, using this package, but I lack one functionality that my code needs, which is the method: “.once("message",() => {})”. I use this to send crypto orders and get their respective message right after.

Anyone have ideas on how to achieve that?

I need to follow one pipeline of: send data to ws server -> get the message and send new data -> get message and send -> … and so on until I achieve the end(I usually do this around 4 times), which is a variable full of specific data for my app.

Searching through the “reconnecting-websocket” lib I found no “once” method.

I really appreciate if anyone can help me.

[makyen]

@regisfaria You haven’t mentioned the actual environment in which you are running your code, so there’s no way for me to know that or address any issues. There’s also no way for me to determine if your IDE is providing you with the actual signature for the method being called, which it may or may not be accurately displaying (i.e. such things are wrong from time to time, don’t assume 100% accuracy).

If you’re using Node.js, then it looks like {once: true} was added in 14.5.0, which was released on 2020-06-30. If you’re using Deno, then {once: true} was added in 1.0, which was released on 2020-05-13. Beyond those, I don’t have much information.

Reconnecting-websocket merely uses .bind() to use all features of the underlying event features:

        // Expose the API required by EventTarget

        this.addEventListener = eventTarget.addEventListener.bind(eventTarget);
        this.removeEventListener = eventTarget.removeEventListener.bind(eventTarget);
        this.dispatchEvent = eventTarget.dispatchEvent.bind(eventTarget);

So, if the {once: true} feature is available in the environment you’re running in will depend entirely on that environment. Using {once: true} definitely works with reconnecting-websocket in browsers.

As I mentioned, {once: true} is just a convenience. It doesn’t add anything which can’t be done with only .addEventListener() and .removeEventListener(). The other answers on the question to which I linked give multiple examples of how you can accomplish this with just those methods and without .once() or {once: true}.

Overall, I wouldn’t support doing any work within reconnecting-websocket to polyfill support for some type of once feature, given that it already works if available in the underlying environment. If it really isn’t available in the environment you’re using and upgrading the environment isn’t an option, then you could add/load a polyfill (seems like overfill), or just use a few lines of code to implement the feature within the event handlers where you’re wanting to use it.

[makyen]

Something like .once() is merely a convenience function that puts a wrapper around whatever listener you’re adding which removes itself and your listener after a single event. As long as you have a way to add listeners and remove listeners, then there is absolutely no reason you can’t implement a similar feature within your event listener, or even an actual .once(), yourself. There’s no need to push something like that down into a low level implementation.