How do I check if the key pressed on a form field is a digit (0 - 9)?

Question

I'm using the onkeyup event on a form field in JavaScript, and I'm wanting to check if the key the key pressed is a numeric digit - i.e. 0 - 9, so I can then do something with the input.

<input type="text" onkeyup="" />

Would I need to use Regex for this?

Answer 1

Use event.key to get the actual value. To check if integer, just use isFinite

input.addEventListener("keydown", function(event) {
    const isNumber = isFinite(event.key);
});

Other option:

const isNumber = /^[0-9]$/i.test(event.key)

An easier HTML solution would be to use the number type input. It restricts to only numbers (kind of).

<input type="number">

Either way, you should clean all user input with:

string.replace(/[^0-9]/g,'');