class ObserverList {
  constructor() {
    this.observerList = [];
  }

  add(obj) {
    return this.observerList.push(obj);
  }

  count() {
    return this.observerList.length;
  }

  get(index) {
    if( index > -1 && index < this.observerList.length ){
      return this.observerList[ index ];
    }
  }

  indexOf(obj, startIndex) {
    let i = startIndex;

    while( i < this.observerList.length ){
      if( this.observerList[i] === obj ){
        return i;
      }
      i++;
    }

    return -1;
  }

  removeAt(index) {
    this.observerList.splice( index, 1 );
  }
}