title: Install Yii2 extension manually without using Composer
body: <p>I want to install <a href="https://github.com/kartik-v/yii2-widget-select2">Select 2 extension</a> widget manually with Yii2 Framework without using composer.</p>
  
  <p>I done the following steps but it's not working.</p>
  
  <p><strong>1)</strong> Added <code>yii2-widget-select2</code> to <code>vendor/yii-soft</code></p>
  
  <p><strong>2)</strong> Added following code in my <code>yii-soft/extensions.php</code>:</p>
  
  <pre><code>'yiisoft/yii2-widget-select2' =&gt; array(
      'name' =&gt; 'yiisoft/yii2-widget-select2',
      'version' =&gt; '2.0.3.0',
      'alias' =&gt;
      array(
          '@yii/kartik' =&gt; $vendorDir . '/yiisoft/yii2-widget-select2',
      ),
  ),
  </code></pre>
  
  <p><strong>3)</strong> Added display in view form: </p>
  
  <pre><code>use kartik\select2\Select2;
  
  &lt;?php echo Select2::widget([
      'model' =&gt; $model,
      'attribute' =&gt; 'state_2',
      'data' =&gt; $data,
      'options' =&gt; ['placeholder' =&gt; 'Select a state ...'],
      'pluginOptions' =&gt; [
          'allowClear' =&gt; true,
      ],
  ]); ?&gt;
  </code></pre>
  
  <p>And It shows the following error:</p>
  
  <blockquote>
    <p>PHP Fatal Error – yii\base\ErrorException. Class
    'kartik\select2\Select2' not found</p>
  </blockquote>