[解決済み] クローンやIDを変更する方法は？

$('#cloneDiv').click(function(){


  // get the last DIV which ID starts with ^= "klon"
  var $div = $('div[id^="klon"]:last');

  // Read the Number from that DIV's ID (i.e: 3 from "klon3")
  // And increment that number by 1
  var num = parseInt( $div.prop("id").match(/\d+/g), 10 ) +1;

  // Clone it and assign the new ID (i.e: from num 4 to ID "klon4")
  var $klon = $div.clone().prop('id', 'klon'+num );

  // Finally insert $klon wherever you want
  $div.after( $klon.text('klon'+num) );

});

<script src="https://code.jquery.com/jquery-3.1.0.js"></script>

<button id="cloneDiv">CLICK TO CLONE</button> 

<div id="klon1">klon1</div>
<div id="klon2">klon2</div>

const all = document.querySelectorAll('[id^="klon--"]');
const maxID = Math.max.apply(Math, [...all].map(el => +el.id.match(/\d+$/g)[0]));
const nextId = maxID + 1;

console.log(`New ID is: ${nextId}`);

<div id="klon--12">12</div>
<div id="klon--34">34</div>
<div id="klon--8">8</div>