JSFiddle - React, Tailwind, and code Playground

by sebababi

HTML

<input type="text" id="theNumber" name="theNumber" size="3"
       onkeypress="return validKey(event || window.event, '0123456789');"
/>

JavaScript

function validKey(e, whitelist) {
    var char = String.fromCharCode(e.which).toLowerCase();
    whitelist = whitelist.toLowerCase();
    if (whitelist.indexOf(char) !== -1)
        return true;
    return false;
}