Javascript-how can I play the next one when I click the Next button in my javascript code?

I made a random playback, and then used to traverse the asynchronous return of the song data. The effect was to click the left and right buttons to play the last and next song, but the result is to click the button on the left to directly play the first one, and when you click the right button, the last one is played directly. who can help you... I made a random playback, and then used to traverse the asynchronous return of the song data. The effect was to click the left and right buttons to play the last and next song, however, the result is to click the button on the left to directly play the first one, and then click the right button to play the last one. who can help me solve the problem? the code is as follows:

    
      
      
          
           
 
 
 
                 
 
  
  
 
   
 
   
 
  
                     
  
  
 
   
 
   
 
   
 
  
                     
                 
             
             
 
  
  

    Song order