Is it possible that someone please tell me what am I doing wrong in here ?
Hello:)
You already have the index of the current song ( currentSongIndex).
You have to add 1 to this and this way you will get the index of the next song. Then with this value you have to check whether there is a song at all in the userData object, with the songs key.
Then with strict equality (===) you have to check that it is defined or undefined.
I tried your code and it works, just one little typo here.
You need to use nextSongExists not nextsongExit.
Thank you very much Mostafa you save my day 
Just typing mistake took my several hours