Ytukyg

I have a situation. I use Node.js to connect to a special hardware. let assume that I have two functions to access the hardware.

hardware.send('command');

hardware.on('responce', callback);

At first, I made a class to interface this to the application layer like this (I write simplified code over here for better understanding)

class AccessHardware {

    constructor() {    

    }

    updateData(callback) {        

        hardware.on('responce', callback);        

        hardware.send('command');

    }

}

Now, the problem is that if there are multiple requests from the application layer to this access layer, they should not send multiple 'command' to the hardware. Instead, they should send one command and all of those callbacks can be served once the hardware answer the command.

So I update the code something like this:

class AccessHardware {

    constructor() {

        this.callbackList = ;

        hardware.on('responce', (value) => {

            while (this.callbackList.length > 0) {

                this.callbackList.pop()(value);

            }

        });        

    }

    updateData(callback) {  

        if (this.callbackList.length == 0) {                    

            hardware.send('command');

        }

        this.callbackList.push(callback);

    }

}

Of course, I prefer to use promise to handle the situation. so what is your suggestion to write this code with promise?
Next question, is this approach to make a 'list of callbacks' good?

I prefer to use promise to handle the situation. So what is your suggestion to write this code with promise?

You'd store a promise in your instance that will be shared between all method callers that want to share the same result:

class AccessHardware {

    constructor(hardware) {

        this.hardware = hardware;

        this.responsePromise = null;

    }

    updateData() {  

        if (!this.responsePromise) {

            this.responsePromise = new Promise(resolve => {

                this.hardware.on('responce', resolve);

                this.hardware.send('command');

            });

            this.responsePromise.finally(() => {

                this.responsePromise = null; // clear cache as soon as command is done

            });

        }       

        return this.responsePromise;

    }

}

Btw, if hardware is a global variable, there's no reason to use a class here.

Is the current solution to make a 'list of callbacks' good?

Yes, that's fine as well for a non-promise approach.