title: Substract half of div width with js
body: <p>I'm new using JS and I'm having troubles with a simple action:</p>
  
  <p>First <code>div</code> is 50% width</p>
  
  <p>I'm looking to subtract from its width the 50% of a Second div using JS.</p>
  
  <p>Would be like:</p>
  
  <pre><code>a_div width = 50% - ( 50% width of b_div)
  </code></pre>
  
  <p>I've tried this but it's not working</p>
  
  <pre><code>$(document).ready(function(){
      $("#h-prev").css({'width':($(".swiper-slide-prev").innerWidth())}).css('width:'-$(".swiper-slide-prev").width() * .50);
      });
  </code></pre>