$.throttle = jq_throttle = function( delay, no_trailing, callback, debounce_mode ) {
    // After wrapper has stopped being called, this timeout ensures that
    // `callback` is executed at the proper times in `throttle` and `end`
    // debounce modes.
    var timeout_id,

      // Keep track of the last time `callback` was executed.
      last_exec = 0;

    // `no_trailing` defaults to falsy.
    if ( typeof no_trailing !== 'boolean' ) {
      debounce_mode = callback;
      callback = no_trailing;
      no_trailing = undefined;
    }

    // The `wrapper` function encapsulates all of the throttling / debouncing
    // functionality and when executed will limit the rate at which `callback`
    // is executed.
    function wrapper() {
      var that = this,
        elapsed = +new Date() - last_exec,
        args = arguments;

      // Execute `callback` and update the `last_exec` timestamp.
      function exec() {
        last_exec = +new Date();
        callback.apply( that, args );
      };

      // If `debounce_mode` is true (at_begin) this is used to clear the flag
      // to allow future `callback` executions.
      function clear() {
        timeout_id = undefined;
      };

      if ( debounce_mode && !timeout_id ) {
        // Since `wrapper` is being called for the first time and
        // `debounce_mode` is true (at_begin), execute `callback`.
        exec();
      }

      // Clear any existing timeout.
      timeout_id && clearTimeout( timeout_id );

      if ( debounce_mode === undefined && elapsed > delay ) {
        // In throttle mode, if `delay` time has been exceeded, execute
        // `callback`.
        exec();

      } else if ( no_trailing !== true ) {
        // In trailing throttle mode, since `delay` time has not been
        // exceeded, schedule `callback` to execute `delay` ms after most
        // recent execution.
        //
        // If `debounce_mode` is true (at_begin), schedule `clear` to execute
        // after `delay` ms.
        //
        // If `debounce_mode` is false (at end), schedule `callback` to
        // execute after `delay` ms.
        timeout_id = setTimeout( debounce_mode ? clear : exec, debounce_mode === undefined ? delay - elapsed : delay );
      }
    };
    if ( $.guid ) {
      wrapper.guid = callback.guid = callback.guid || $.guid++;
    }
    return wrapper;
  };


$.fn.isInViewport = function() {
  var elementTop = $(this).offset().top;
  var elementBottom = elementTop + $(this).outerHeight();
  var viewportTop = $(window).scrollTop();
  var viewportBottom = viewportTop + $(window).height();
   let percent = (($(this).height() - (viewportBottom - elementBottom)) / $(this).height())*100;
  return elementBottom > viewportTop && elementTop < viewportBottom && percent >= 59 && percent <= 160;

};

$('.content').on('resize scroll', $.throttle(200,function() {
  let reviewsView = $('#reviews').isInViewport() ;
  let tariffsView = $('#tariffs').isInViewport();
  let topView = $('#top').isInViewport() || $('#how-it-works').isInViewport() || $('.for-what').isInViewport() ;
if (!reviewsView && !tariffsView && !topView){
  return
}
$('.active').removeClass('active')
reviewsView?$("a[href$='/#reviews']").addClass('active'):'';
tariffsView?$("a[href$='/#tariffs']").addClass('active'):'';
topView?$("a[href$='/#top']").addClass('active'):'';
}));