DataTable Excel export issue

by matthew__b

HTML

<!DOCTYPE html>
<html>
  <head>
    <link href="https://bootswatch.com/4/sandstone/bootstrap.css" rel="stylesheet" />
    <link href="https://cdn.datatables.net/1.10.19/css/dataTables.bootstrap4.min.css" rel="stylesheet" />
    <link href="https://cdn.datatables.net/buttons/1.5.4/css/buttons.bootstrap4.css" rel="stylesheet" />
    <link href="https://cdn.datatables.net/fixedheader/3.1.5/css/fixedHeader.bootstrap4.min.css" rel="stylesheet" />
    
    <meta charset=utf-8 />
    <title>DataTables - JS Bin</title>
  </head>
  <body>
    <nav class="navbar navbar-expand-lg navbar-dark bg-dark">
      <a class="navbar-brand" href="#">Site Name</a>
      <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
          <span class="navbar-toggler-icon"></span>
      </button>
    </nav>
    
    <div class="container">
      <table id="example" class="table table-bordered table-striped" width="100%">
        <thead>
          <tr>
            <th>Name</th>
            <th>Position</th>
            <th>Office</th>
            <th>Age</th>
            <th>Start date</th>
            <th>Salary</th>
          </tr>
        </thead>

        <tfoot>
          <tr>
            <th>Name</th>
            <th>Position</th>
            <th>Office</th>
            <th>Age</th>
            <th>Start date</th>
            <th>Salary</th>
          </tr>
        </tfoot>

        <tbody>
          <tr>
            <td>Tiger Nixon</td>
            <td>System Architect</td>
            <td>Edinburgh</td>
            <td>61</td>
            <td>2011/04/25</td>
            <td>$3,120</td>
          </tr>
          <tr>
            <td>Garrett Winters</td>
            <td>Director</td>
            <td>Edinburgh</td>
            <td>63</td>
            <td>2011/07/25</td>
            <td>$5,300</td>
          </tr>
          <tr>
           ...

JavaScript

$(document).ready( function () {
  var table = $('#example').DataTable({
        dom: "Bfrtip",
        buttons: [
          "excelHtml5"
        ],
        pageLength: 100,
        fixedHeader: {
            headerOffset: $("#navbar").outerHeight()
        }
    });
} );