JSFiddle - React, Tailwind, and code Playground

by Qwerty_Wasd

HTML

<form name="myform">
    <input type="text" id="cardcode">
</form>

JavaScript

for (var i in ['input', 'change', 'blur', 'keyup']) {
    cardcode.addEventListener('input', formatCardCode, false);
}
function formatCardCode() {
    var cardCode = this.value.replace(/[^\d]/g, '').substring(0,8);
    cardCode = cardCode != '' ? cardCode.match(/.{1,2}/g).join('/') : '';
    this.value = cardCode;
}