Sharepoint 2013 left quick navigation accordion by JQuery

for testing add this below code to your Script Editor web part.


<script>
$(function(){
 /*set dynamic css logic*/
 if($('#sideNavBox .menu-item.selected').length){
  //propagates the selected class, up the three.
  $('li.static').removeClass('selected');
  $('#sideNavBox .menu-item.selected').parents('li.static').addClass('selected');

  //collapses top siblings of selected branch
  $('#sideNavBox .menu-item.selected').parents('li.static').last().siblings()
   .find('> ul').hide();
 }
 else $('#sideNavBox .root.static > li.static > ul').hide();

 /*set accordion effect*/
 $('#sideNavBox .root.static > li.static').each(function(){
  if($(this).find('ul').length){
   $(this).addClass('father').click(function(){
    if($(this).children('ul').css('display') != 'none'){
     $(this).removeClass('selected').children('ul').slideUp();
    }
    else {
     /*collapse-siblings*/
     $(this).siblings().removeClass('selected').children('ul').slideUp();

     /*expand*/
     $(this).addClass('selected').children('ul').slideDown();
    }

    /*added: stop event propagation to link nodes*/
    $('a.static').click(function(event) {
        event.stopPropagation();
    });

    /*added*/
    return false;
   });
  }
 });
});

</script>

Referenced from: http://borderingdotnet.blogspot.in/2013/04/accordion-left-navigation-for.html

---------- updated on 5-march-2018-----

$(function(){
 /*set dynamic css logic*/
 if($('#sideNavBox .menu-item.selected').length){
  //propagates the selected class, up the three.
  $('li.static').removeClass('selected');
  $('#sideNavBox .menu-item.selected').parents('li.static').addClass('selected');

  //collapses top siblings of selected branch
  $('#sideNavBox .menu-item.selected').parents('li.static').last().siblings()
   .find('> ul').hide();
 
   $('a.static').click(function(event) {
        event.stopPropagation();
    });
 }
 else $('#sideNavBox .root.static > li.static > ul').hide();

 /*set accordion effect*/
 $('#sideNavBox .root.static > li.static').each(function(){
  if($(this).find('ul').length){
   $(this).addClass('father').click(function(){
    if($(this).children('ul').css('display') != 'none'){
     $(this).removeClass('selected').children('ul').slideUp();
    }
    else {
     /*collapse-siblings*/
     $(this).siblings().removeClass('selected').children('ul').slideUp();

     /*expand*/
     $(this).addClass('selected').children('ul').slideDown();
    }

    /*added: stop event propagation to link nodes*/
    $('a.static').click(function(event) {
        event.stopPropagation();
    });

    /*added*/
    return false;
   });
  }
 });

});