title: get all the text inside HTML span tag and clustering it using javascript
body: <p>I have HTML text like: </p>
  
  <pre><code>&lt;span class="c1" &gt; text1  text2  text3 &lt;/span&gt; text4 text5 text6...
  &lt;span class="c2" &gt; text8  text9  text10 &lt;/span&gt; text14 text15 text16...
  &lt;span class="c1" &gt; text18  text19  text20 &lt;/span&gt; text21
  </code></pre>
  
  <p>I would like to have a result like that:</p>
  
  <p>C1: text1  text2  text3 + text18  text19  text20 </p>
  
  <p>C2: text8  text9  text10</p>
  
  <p>which mean clustering text by span
  How can i do this in Javascript</p>