EventEmitter ES6

EventEmitter.js

class EventEmitter{
  constructor(selector){
    this.cb = new Map();
  }
  on(e,f){
    var cb;
    if(!this.cb.has(e))
      this.cb.set(e, cb = new Set());
    else
      cb = this.cb.get(e);
    cb.add(f);
    console.log(e,f,cb,this.cb);
  }
  once(e,f){
    var off = ()=>{
      this.off(e,f);
      this.off(e,off);
    }
    this.on(e,f);
    this.on(e,off);
  }
  off(e,f){
    if(!f){
      delete this.cb.delete(e);
      return;
    }
    var cb = this.cb.get(e);
    if(cb)
      cb.delete(f);
  }
  emit(e,...args){
    var cb = this.cb.get(e);
    if(!cb)
      return;
    cb.forEach(f=>f(...args));
  }
}