Why is this while loop iterating infinitely?

Question

This while loop should have terminated when it encountered the *,as parseInt(num[1])=NaN.Bu it keeps on iterating.Whys?

 var num=["1","*","2","3","4"]
    var index=4
    var eachop=1;
    
     while((parseInt(num[index]))!=NaN){
                 num[index]=eachop;
                index=index-1;
               console.log(index);
                            
                        }