EventTarget

class EventTarget {
  constructor(options) {
  	if(options) {
	  Object.assign(this, options);
	}
  	this.listeners = {};
  }

  addEventListener (type, callback, useCaptureOptions) {
    if (!(type in this.listeners)) {
      this.listeners[type] = [];
    }
    this.listeners[type].push([callback, useCaptureOptions]);
    return this.removeEventListener.bind(this, type, callback, useCaptureOptions);
  };

  removeEventListener(type, callback, useCaptureOptions) {
    if (!(type in this.listeners)) {
      return;
    }
    var stack = this.listeners[type];
    for (let cbsarr of stack) {
    	const [cb, uco] = cbsarr;
      if (cb === callback){
      	const useCaptureOptionsKeys = Object.keys(useCaptureOptions);
        const ucoKeys = Object.keys(uco);
        if(useCaptureOptionsKeys.length === ucoKeys.length &&
        	useCaptureOptionsKeys.every(k => useCaptureOptionsKeys[k] === ucoKeys[k])) {
            stack.splice(i, 1);
        		return;
          }
      }
    }
  };

  dispatchEvent(event) {
    if (!(event.type in this.listeners)) {
      return true;
    }
    const stack = this.listeners[event.type].slice();

    for (let [cb, useCaptureOptions = {}] of stack) {
    	const { capture = (useCaptureOptions === true), once = false, passive = false } = useCaptureOptions;
      cb.call(this, event, {
      	capture,
        once,
        passive
      });
      if(once) {
      	this.removeEventListener(event.type, cb, useCaptureOptions);      	
      }
    }
    return !event.defaultPrevented;
  };

}