can i know a reason of the fail of my coding?

Question

I made the code like this but it doesn't work. I can't see any output although I can see the prompt box can I know a reason??

var age = prompt("enter your age");
var isAdult = (age <18) ? "Too young": (age <30) ? "middle": (age <40)? "last": (age <50) ? "old":