title: jQuery offset().left vs offsetLeft
body: <p>Currently I'm trying to speedup my code with refactoring from <strong>jQuery</strong> to <strong>pure JS</strong>.</p>
  
  <p>I know that there are some other threads about this, but I couldn't find any which is equals to my problem.</p>
  
  <p>Now I'm at the point where I want to get the same value with <code>offsetLeft</code> instead using <code>offset().left</code></p>
  
  <p>Does anyone know a simple explanation how to calculate the right value?</p>