How To Make Random Level With Addlevel Api In Bb3?

i tried this code but didn't work :/
how can i make random 1 random level, then specific level then random again and finally game end level.

let levelname = Math.random()*45;;
this.scene().addLevel(String(levelname));
this.scene().addLevel('empty');
this.scene().addLevel(String(levelname));
this.scene().addLevel('empty');
this.scene().addLevel(String(levelname));
this.scene().addLevel('empty');
this.scene().addLevel(String(levelname));
this.scene().addLevel('empty');
this.scene().addLevel(String(levelname));
this.scene().addLevel('empty');
this.scene().addLevel(String(levelname));
this.scene().addLevel('empty');
this.scene().addLevel(String(levelname));
this.scene().addLevel('empty');
this.scene().addLevel(String(levelname));
this.scene().addLevel('empty');
this.scene().addLevel('finish');
this.scene().addLevel('empty');