Event Handler Namespace in Vanilla JavaScript

In this solution I've extended the DOM to have on and off methods with the ability to use events namespacing:

var events = {
  on(event, cb, opts){
    if( !this.namespaces ) // save the namespaces on the DOM element itself
      this.namespaces = {};

    this.namespaces[event] = cb;
    var options = opts || false;
    
    this.addEventListener(event.split('.')[0], cb, options);
    return this;
  },
  off(event) {
    this.removeEventListener(event.split('.')[0], this.namespaces[event]);
    delete this.namespaces[event];
    return this;
  }
}

// Extend the DOM with these above custom methods
window.on = Element.prototype.on = events.on;
window.off = Element.prototype.off = events.off;


window
  .on('mousedown.foo', ()=> console.log("namespaced event will be removed after 3s"))
  .on('mousedown.bar', ()=> console.log("event will NOT be removed"))
  .on('mousedown.baz', ()=> console.log("event will fire once"), {once: true});

// after 3 seconds remove the event with `foo` namespace
setTimeout(function(){
    window.off('mousedown.foo')
}, 3000)

Click anywhere 

I think you are looking for addEventListener and removeEventListener. You can also define custom events and fire them using dispatchEvent.

However, to remove an event listener, you will need to retain a reference to the event function to remove just the function you want to remove instead of clearing the whole event.

For anyone still looking for this, I ended up making a helper singleton which keeps track of the function references for me.

class EventHandlerClass {
  constructor() {
    this.functionMap = {};
  }

  addEventListener(event, func) {
    this.functionMap[event] = func;
    document.addEventListener(event.split('.')[0], this.functionMap[event]);
  }

  removeEventListener(event) {
    document.removeEventListener(event.split('.')[0], this.functionMap[event]);
    delete this.functionMap[event];
  }
}

export const EventHandler = new EventHandlerClass();

Then just import EventHandler and use like:

EventHandler.addEventListener('keydown.doop', () => console.log("Doop"));
EventHandler.addEventListener('keydown.wap', () => console.log("Wap"));
EventHandler.removeEventListener('keydown.doop');
// keydown.wap is still bound