Update player-bar.js

scripts/player-bar.js

@@ -14,4 +14,17 @@
     const nextSong = album.songs[nextSongIndex];
     player.playPause(nextSong);
   });
+
+  $('button#previous').on('click', function() {
+    if (player.playState !== 'playing') { return; }
+
+
+    const currentSongIndex = album.songs.indexOf(player.currentlyPlaying);
+    const previousSongIndex = currentSongIndex - 1;
+    if (currentSongIndex == 0) { return; }
+
+    const previousSong = album.songs[previousSongIndex];
+    player.playPause(previousSong);
+  });
+
 }