JSFiddle - React, Tailwind, and code Playground

by bg100

JavaScript

let aidmac = "12:34:56789abc";

aidmac = aidmac.toUpperCase().replace(/[^0123456789ABCDEF]/g, "");
if (aidmac.length !== 12) console.log("err");
aidmac = aidmac.replace(/(..)/g, "$1:");
aidmac = aidmac.substr(0, aidmac.length - 1);

console.log(aidmac);