jQuery: animate opacity on slideToggle

script-full.js

/**
    * UDBrand header
    * http://stackoverflow.com/questions/21918477/jquery-toggle-opacity-on-click-using-css-animation
    * http://stackoverflow.com/questions/18995647/jquery-make-global-variable
 */
var current_width;
var pixel_ratio;
var logo_big;

$('#searchdiv').on('click', function(e){
     $('.dropDown').slideToggle(300);
      if ( current_width < 768) {
  logo_big = $('#ud_primary_logo_big');
  // logo_big is not visible lets make it visible.
  if(logo_big.css('opacity') === '0')  {
    logo_big.animate({
      opacity: '1',
      width: '177px'
    });
  }
  else {
   logo_big.animate({
      opacity: '0',
      width: '0'
    });
  }
}