JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <thead>
    <tr id="mq">
        <td><input type="checkbox" /></td>
        <td>firstname</td>
        <td>secondname</td>
        <td>lastname</td>
    </tr>
    </thead>
    <tbody>
        <tr id="1">
        <td><input type="checkbox" /></td>
        <td>lorem</td>
        <td>ipsum</td>
        <td>css</td>
        </tr>
        <tr id="2">
        <td><input type="checkbox"  /></td>
        <td>lorem</td>
        <td>ipsum</td>
        <td>css</td>
        </tr>
        <tr id="3">
        <td><input type="checkbox" /></td>
        <td>lorem</td>
        <td>ipsum</td>
        <td>css</td>
        </tr>
        <tr id="4">
        <td><input type="checkbox" /></td>
        <td>lorem</td>
        <td>ipsum</td>
        <td>css</td>
        </tr>
        <tr id="5">
        <td><input type="checkbox"  /></td>
        <td>lorem</td>
        <td>ipsum</td>
        <td>css</td>
        </tr>
    </tbody>
</table>
<button id="thechecked">Get Checked</button>

CSS

tr,td{border:1px solid black;}

JavaScript

(function( $ ){
      $.fn.checkedList = function(){
          var closestTr = $(':checkbox:checked').closest('tr').attr('id');
          /**
            return $.map( this, function (elem) {
                  return elem.value || "";
            }).join( "," );
      };
      */
})( jQuery );

var closestTr = $(':checkbox:checked').closest('tr').attr('id');
alert(closestTr);