text: 
  const initialState= {
  	index:0,
  	videos:[
  	'https://www.youtube.com/embed/MhkGQAoc7bc',
  	'https://www.youtube.com/embed/i9MHigUZKEM',
  	'https://www.youtube.com/embed/4WJLlWpzpP0']
  };
  
  const handlers={
    'PLAY_NEXT':(state,action)=>({index:state.index+1})
    ,'PLAY_PREVIOUS':(state,action)=>({index:state.index-1})
    ,'ADD_VIDEO':(state,action)=>({videos:addVideo(state,action.value)})
  }
  
  function addVideo (state,data) {
  		state.videos.push(data);
  		return state.videos;
  }
  export default function activityReducer (state = initialState, action) {
    let handler = handlers[action.type];
    if (!handler) return state;
    return { ...state, ...handler(state, action) };
  }