JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.6-rc.0/css/select2.min.css">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/select2-bootstrap-theme/0.1.0-beta.10/select2-bootstrap.min.css">
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.6-rc.0/js/select2.min.js"></script>
<ul class="nav nav-tabs" id="myTab" role="tablist">
  <li class="nav-item">
    <a class="nav-link active" id="home-tab" data-toggle="tab" href="#home" role="tab" aria-controls="home" aria-selected="true">Home</a>
  </li>
  <li class="nav-item">
    <a class="nav-link" id="profile-tab" data-toggle="tab" href="#profile" role="tab" aria-controls="profile" aria-selected="false">Profile</a>
  </li>
  <li class="nav-item">
    <a class="nav-link" id="contact-tab" data-toggle="tab" href="#contact" role="tab" aria-controls="contact" aria-selected="false">Contact</a>
  </li>
</ul>
<div class="tab-content" id="myTabContent">
  <div class="tab-pane fade show active" id="home" role="tabpanel" aria-labelledby="home-tab">...</div>
  <div class="tab-pane fade" id="profile" role="tabpanel" aria-labelledby="profile-tab">
    
            <div class="form-group">
                <label for="selectClientMapping">Nachfolgend können Sie die zugeordneten Computer auswählen:</label>
                <select class="selectMapping form-control select2-multiple" name="selectClientMapping[]" id="selectClientMapping" multiple="multiple" style="width: 100%">
                    <option value="1">Tust</option>";
                </select>
            </div>    
    
  </div>
  <div class="tab-pane...

JavaScript

$(document).ready(function() {
    $('.selectMapping').select2({
	    theme: "bootstrap",
        placeholder: 'Bitte auswählen ...',
        allowClear: true
	});
});