How do I restrict a number with JavaScript

Question

<label for="fname">Name</label>
<input type="number" id="fname" name="firstname" placeholder="Your name.." required>

<button onclick="f()">Try it</button>

var x = [10, 11];
function f() {
document.getElementById("fname");
if (x == true) {
alert("cant use such number");
}
else {
alert("cool");
}
}

What do I do when I don’t want some specific numbers to be inputted

Answer 1

Exist an range input type that do this:

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/range

Answer 2

Doesn’t lucid. I want to do it with JavaScript