Why Javascript else statement is not returning the value? [duplicate]

So I am a beginner at Javascript so please help me understand this!

I was just testing out different things with if/else and prompt(), and when I wrote the codes below:

let ask = Number(prompt("Type a number"));

if (ask != NaN) {
  alert(`You typed ${ask}`);
} else {
  alert("You typed a word")
}

so the code is working well until I type in a word. when I type a number (for instance: 12) it shows "You type 12" but when I typed a word (for instance "cat"), it shows "You typed NaN". but why? I know "cat" is a NaN but why is it not showing the else statement? (You typed a word).

please help!