<ul>
  <li>
    <h3>Market study</h3>
    <div>
      <a href="#" data-toggle="#div1" class="showSingle">Results</a>
      <a href="#" data-toggle="#div2" class="showSingle">Learned</a>
      <a href="#" data-toggle="#div3" class="showSingle">Deliverables</a>
      <a href="#" data-toggle="#close" class="">Close all</a>
      <div id="div1" class="optionDiv">Results: </div>
      <div id="div2" class="optionDiv">Learned: </div>
      <div id="div3" class="optionDiv">Deliverables: </div>
    </div>
  </li>
  <li>
    <h3>Competitive research</h3>
    <div>
      <a href="#" data-toggle="#div1" class="showSingle">Results</a>
      <a href="#" data-toggle="#div2" class="showSingle">Learned</a>
      <a href="#" data-toggle="#div3" class="showSingle">Deliverables</a>
      <a href="#" data-toggle="#close" class="">Close all</a>
      <div id="div1" class="optionDiv">Results: </div>
      <div id="div2" class="optionDiv">Learned: </div>
      <div id="div3" class="optionDiv">Deliverables: </div>
    </div>
  </li>
</ul>

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    var myIndex = $(this).index();

    if (idOpen.is("div")) {
      // HIDE ALL DIVS IN PARENT
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      for (var i = 0, l = divLength; i < l; i++) {
        console.log('divs to hide', idOpen[i]);
        //HIDE DOESN'T WORK
        //idOpen[i].hide();
      }

      // HOW TO SHOW LINKED DIV ???
      console.log('div id to open: ', idOpen.get(myIndex).id);
    }

  })