title: open/close sidenav bar same button
body: <p>I have a button that I'm hoping will open and close a side nav.  My button code is:</p>
  
  <pre><code>&lt;button class="myBtn" id="myBtn"&gt;&lt;i class="glyphicon glyphicon-info-sign"&gt;&lt;/i&gt;&lt;/button&gt; 
  </code></pre>
  
  <p>I'm trying to use addEventListener and think i may be missing an if statement in this, but can't be sure:</p>
  
  <pre><code>document.getElementById("myBtn").addEventListener("click", open);
      function open() {
          document.getElementById("mySidenav").style.width = "250px";
          document.getElementById("main").style.marginLeft = "250px";
          document.body.style.backgroundColor = "rgba(0,0,0,0.4)";
  }
  document.getElementById("myBtn").addEventListener("click", close);
      function close() {
           document.getElementById("mySidenav").style.width = "0";
          document.getElementById("main").style.marginLeft = "0";
          document.body.style.backgroundColor = "white";
  } 
  </code></pre>
  
  <p>any suggestions?  thanks!</p>