music-player/src/reducers/playerReducer.js

export function playerReducer(state={},{
    type,
    isPlaying=false,
    isStopped,
    duration,
    track,
    // playlist: {_id, name, tracks},
    playlistIndex,
    currentTime=0,
    volume,
}) {

    if (type === 'TRACK_PLAY') {
        return {
            ...state,
            isPlaying,
            isStopped: !isPlaying,
        };
    }
    if (type === 'TRACK_STOP') {
        return {
            ...state,
            isStopped,
            isPlaying: !isStopped,
        };
    }

    return state
}

export const actionTrackPlay = (track,isPlaying) => ({type: "TRACK_PLAY",isPlaying: track.play()})
export const actionTrackStop = (track,isStopped) => ({type: "TRACK_PLAY",isStopped: track.pause()})