Check if input is number or letter javascript

Question

I\'m using forms in HTML and javascript. I would like an alert to pop up only if the user inputs a LETTER and clicks submit.

So I have

Answer 1

you can use isNaN(). it returns true when data is not number.

var data = 'hello there';
if(isNaN(data)){
  alert("it is not number");
}else {
  alert("its a valid number");
}