JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.aspnetcdn.com/ajax/jquery.dataTables/1.9.0/css/jquery.dataTables.css">
<script src="http://ajax.aspnetcdn.com/ajax/jquery.dataTables/1.9.0/css/jquery.dataTables_themeroller.css "></script>
<script src="http://datatables.net/release-datatables/media/js/jquery.js"></script>
<script src="http://datatables.net/release-datatables/media/js/jquery.dataTables.js"></script>
<script src="http://datatables.net/release-datatables/extras/FixedColumns/media/js/FixedColumns.js"></script>
<body>
   <div class="container">
      <table width="100%" cellpadding="0" cellspacing="0" border="1" id="example">
         <thead>
            <tr>
               <th rowspan="2">Branch</th>
               <th rowspan="2">Object</th>
               <th rowspan="2">Address</th>
               <th rowspan="2">Cnt</th>
               <th colspan="7">Availability</th>
            </tr>
            <tr>
               <th>15</th>
               <th>16</th>
               <th>17</th>
               <th>18</th>
               <th>19</th>
               <th>20</th>
               <th>21</th>
            </tr>
         </thead>
         <tbody>
            <tr>
               <td>United States of America, Washington</td>
               <td>ABC-123</td>
               <td>1514 Amber Pond Highway, Nohead Bottom, Washington, 99205-8224, US, (425) 023-9448</td>
               <td><a href="#">7</a></td>
               <td>-</td><td>-</td><td>-</td>
               <td>-</td><td>-</td><td>-</td><td>-</td>
            </tr>
            <tr>
               <td>United States of America, South Dakota</td>
               <td>DEF-456</td>
               <td>7827 Stony Pointe, Sunsweet, South Dakota, 57006-2156, US, (605) 621-7800</td>
               <td><a href="#">7</a></td>
               <td>-</td><td>-</td><td>-</td>
               <td>-</td><td>-</td><td>-</td><td>-</td>
            </tr>
            <tr>
               <td>United States of America, Newfoundland</td>
...

JavaScript

$(document).ready(function() {    
    var aoColumns = [null,null,null,null,null,null,null,null,null,null,null];
    
    var oTable = $('#example').dataTable( {
        "sScrollX": "100%",
        "sScrollXInner": "150%",
        "bPaginate": false,
        "bAutoWidth": true,
        "aoColumns": aoColumns        
    } );
    
    var oFC = new FixedColumns( oTable, {
        "iLeftColumns": 4
    } );
    
    oTable.fnAdjustColumnSizing();
    
    // *** FIX WIDTHS ON LEFT SIDE ***
    var widths = [];
    
    // first fix widths on tbody ...
    $('.DTFC_LeftBodyWrapper thead th').each(
        function(){
            $(this).css('width', $(this).width());
        });
    
    // ... now save the actual widths on array
    $('.DTFC_LeftBodyWrapper thead th').each(
        function(){ 
            widths.push($(this).width());
        });
    
    // ... now update widths on thead
    $('.DTFC_LeftHeadWrapper thead th').each(
        function(i, val){
            console.log('i:', i, ', width:',  widths[i]);
            $(this).css('width', widths[i]);
        });
});