The title is incorrect, as some users pointed out and you should throw some code snippets to showcase what you've been doing and where exactly your problem is. From the form of the question and details, I would suggest you do some research into the differences between frontend and backend and the solution will be clearer. But regarding your specific issue, assuming you're using Node, probably with Express and some templating engine;

• You'll want to attach a onClick listener to your button in your ejs/pug/haml file
• Get the data from your form in some way, either by getElementById or FormData
• Do a fetch with POST on the endpoint hitting your route -> controller with the data from your form or buttons
• res.json(...) or, more likely res.render(...) your page with the related data result

Check out Node's EventEmitter. With this class, you can emit events and listen for them. You can also create your own classes which extend EventEmitter and make use of its functionality like so:

const { EventEmitter } = require('events');

class MyClass extends EventEmitter {
    constructor() {
        super();
    }

    doSomething() {
        this.emit('someEvent');
    }
}

const test = new MyClass();

test.on('someEvent', () => console.log('event was fired'));

test.doSomething();