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

Use Regular Expression to match for only letters. It's also good to have knowledge about, if you ever need to do something more complicated, like make sure it's a certain count of numbers.

function checkInp()
{
    var x=document.forms["myForm"]["age"].value;
    var regex=/^[a-zA-Z]+$/;
    if (!x.match(regex))
    {
        alert("Must input string");
        return false;
    }
}

Even better would be to deny anything but numbers:

function checkInp()
{
    var x=document.forms["myForm"]["age"].value;
    var regex=/^[0-9]+$/;
    if (x.match(regex))
    {
        alert("Must input numbers");
        return false;
    }
}