Change input field on keyup to match MAC address format

Question

I don't have much experience with JavaScript or jQuery.

I tried to use Tampermonkey to auto correct the input field for a MAC address.

The site wants a MAC address formatted as 00:00:00:00:00:00.

So I wrote this script for Tampermonkey so it automatically adds the colons while I'm typing:

// ==UserScript==
// @name         Name
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Adds colons to the mac adress of the Mac Field
// @author       You
// @match        Somesite
// @grant        none
// @require http://code.jquery.com/jquery-latest.js
// ==/UserScript==
document.getElementById("MAC").addEventListener('keyup', function() { 
  var mac = document.getElementById('MAC').value;
  var macs = mac.split('');
  var colons = ["2", "5", "8", "11", "14"];
  for (var col in colons) {
    if (macs[col] == "-") {
      macs[col] = ":";
    } else if (macs[col] != "") {

    } else if (macs[col] != ":") {
      var colo = col + 1;
      macs[colo] = macs[col];
      macs[col] = ":";
    }
  }
  mac = macs.toString();
});

<input id=MAC />

But it don't work. The ID of the inputfield is MAC.

Where and how much did I do wrong?

SOLUTION

Thanks to @i-wrestled-a-bear-once and @freginold for the , my oppion, best solutions

I'm using now a slightly changed version from @freginold

var back = true;
function isHex(char) {
  // check if char is a hex char
  if (!isNaN(parseInt(char))) {
    return true;
  } else {
    switch (char.toLowerCase()) {
      case "a":
      case "b":
      case "c":
      case "d":
      case "e":
      case "f":
        return true;
    }
    return false;
  }
}
document.getElementById("MAC").addEventListener('keydown', function() {
    var key = event.keyCode || event.charCode;

   if( key == 8 || key == 46 ) {
       back = false;
   }
});

document.getElementById("MAC").addEventListener('keyup', function() {
    var key = event.keyCode || event.charCode;


  var mac = document.getElementById('MAC').value;
  var newMac = mac.replace("-", ""); // remove any dashes
  if ((isHex(mac[mac.length - 1]) && (isHex(mac[mac.length - 2])) && (mac.length <= 16) && (back))) {
    // if last two chars are numbers, insert a colon
    newMac = newMac + ":";

  }
back = true;
  document.getElementById('MAC').value = newMac; // put new value into input field

});

Answer 1

You could simplify it and check if the last two characters in the string are hex characters (0-9, A-F) and if so, insert a :. You can also use .replace() to remove any occurrence of - if you (or someone else) types a dash instead of a colon.

That way you can cover inserting colons if you don't type them at all, as well as converting any typed dashes to colons.

Here's a working example:

// ==UserScript==
// @name         Name
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Adds colons to the mac adress of the Mac Field
// @author       You
// @match        Somesite
// @grant        none
// @require http://code.jquery.com/jquery-latest.js
// ==/UserScript==
function isHex(char) {
  if (!isNaN(parseInt(char))) {
    return true;
  } else {
    switch (char.toLowerCase()) {
      case "a":
      case "b":
      case "c":
      case "d":
      case "e":
      case "f":
        return true;
        break;
    }
    return false;
  }
}

document.getElementById("MAC").addEventListener('keyup', function() {
  var mac = document.getElementById('MAC').value;
  if (mac.length < 2) {
    return;
  }
  var newMac = mac.replace("-", "");
  if ((isHex(mac[mac.length - 1]) && (isHex(mac[mac.length - 2])))) {
    newMac = newMac + ":";
  }
  document.getElementById('MAC').value = newMac;
});

document.getElementById('MAC').focus(); // autofocus for testing

<input id=MAC />