<!DOCTYPE html>
<html>
  <title></title>
  <head>
    <script>
      function getre(pkStr, pkNum) {
        if (pkStr === pkNum) return 'nice try';
        var res = [
          /^\D+/g,
          /\D+$/g,
          /^\D+|\D+$/g,
          /\D+/g,
          /\D.*/g,
          /.*\D/g,
          /^\D+|\D.*$/g,
          /.*\D(?=\d)|\D+$/g,
        ];
        for (var i = 0; i < res.length; i++)
          if (pkStr.replace(res[i], '') === pkNum)
            return 'pkNum = pkStr.replace(/' + res[i].source + '/g, "")';
        return 'no idea';
      }

      function update() {
        $ = function (x) {
          return document.getElementById(x);
        };
        var re = getre($('pkStr').value, $('pkNum').value);
        $('pkRe').innerHTML = 'Numex speaks: <code>' + re + '</code>';
      }
    </script>
  </head>
  <body>
    <p>Hi, I'm praksh, the Number Extractor.</p>
    <p>What is your string? <input id="pkStr" value="42abc"></p>
    <p>What number do you want to extract? <input id="pkNum" value="42"></p>
    <p><button onclick="update()">Insert Coin</button></p>
    <p id="pkRe"></p>
  </body>
</html>