function StringArray (n) {
  this.length = n;
  for (var i =1; i <= n; i++) {
    this[i] = ' '

  }
}
song = new StringArray(5)
song[0] = 'AngelsAndAirwaves-TheAdventure.mp3'
song[1] = 'Frank-Black-You-Aint-Me.mp3'
song[2] = 'HollowMan.mp3'
song[3] = 'ShapeTheSky.mp3'
song[4] = 'Supersonic.mp3'

var randomnumber=Math.floor(Math.random()*song.length);