JSFiddle - React, Tailwind, and code Playground

HTML

<a href="#" onclick="genMAC()">CLICK HERE </a>

JavaScript

function genMAC(){
var colours = new Array("0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F");
// Make variable to hold 6 character HEX array
var partA = new Array(1);
var partB = new Array(1);
var partC = new Array(1);
var partD = new Array(1);
var partE = new Array(1);
var partF = new Array(1);
var mac_address="";
for (i=0;i<2;i++){
    
    // Loop for partA
    partA[i]=colours[Math.round(Math.random()*14)];
}
    for (i=0;i<2;i++){
    // Loop through 6 times, randomising the letter added to the array
    partB[i]=colours[Math.round(Math.random()*14)];
}
    for (i=0;i<2;i++){
    // Loop through 6 times, randomising the letter added to the array
    partC[i]=colours[Math.round(Math.random()*14)];
}
    for (i=0;i<2;i++){
    // Loop through 6 times, randomising the letter added to the array
    partD[i]=colours[Math.round(Math.random()*14)];
}
    for (i=0;i<2;i++){
    // Loop through 6 times, randomising the letter added to the array
    partE[i]=colours[Math.round(Math.random()*14)];
}
    for (i=0;i<2;i++){
    // Loop through 6 times, randomising the letter added to the array
    partF[i]=colours[Math.round(Math.random()*14)];
}
// Returns like "a10bc5". It is likely that you may need to add a "#".
mac_address = partA[0]+ partA[1] + ":" + partB[0]+ partB[1] + ":" + partC[0]+ partC[1] + ":" + partD[0] + partD[1] + ":" + partE[0] + partE[1] + ":" + partF[0] + partF[1];
alert(mac_address);
}