Add Scroll to top before transition start

Js newbie here, so excuse moi the dumb question ;D

Trying to add scrollTop before the transition start in the fade example below (got it on http://barbajs.org/transition.html). Right now this code works but the new page opens on random content.

var FadeTransition = Barba.BaseTransition.extend({
  start: function() {
    /**
     * This function is automatically called as soon the Transition starts
     * this.newContainerLoading is a Promise for the loading of the new container
     * (Barba.js also comes with an handy Promise polyfill!)
     */

    // As soon the loading is finished and the old page is faded out, let's fade the new page
    Promise
      .all([this.newContainerLoading, this.fadeOut()])
      .then(this.fadeIn.bind(this));
  },

  fadeOut: function() {
    /**
     * this.oldContainer is the HTMLElement of the old Container
     */

    return $(this.oldContainer).animate({ opacity: 0 }).promise();
  },

  fadeIn: function() {
    /**
     * this.newContainer is the HTMLElement of the new Container
     * At this stage newContainer is on the DOM (inside our #barba-container and with visibility: hidden)
     * Please note, newContainer is available just after newContainerLoading is resolved!
     */

    var _this = this;
    var $el = $(this.newContainer);

    $(this.oldContainer).hide();

    $el.css({
      visibility : 'visible',
      opacity : 0
    });

    $el.animate({ opacity: 1 }, 400, function() {
      /**
       * Do not forget to call .done() as soon your transition is finished!
       * .done() will automatically remove from the DOM the old Container
       */

      _this.done();
    });
  }
});

/**
 * Next step, you have to tell Barba to use the new Transition
 */

Barba.Pjax.getTransition = function() {
  /**
   * Here you can use your own logic!
   * For example you can use different Transition based on the current page or link...
   */

  return FadeTransition;
};

any idea??

[factorzero]

I also recommend adding this too:

if ('scrollRestoration' in history) {
    history.scrollRestoration = 'manual';
  }

What this does is it prevent Chrome from jumping to the last scroll position when pressing the back button. Without it, even when scrolling to the top of the page with jquery Chrome will remember the last scroll position causing issues with your animation.

[factorzero]

@yelapijo You can scroll to the top of the page before the fade in like this:

  fadeIn: function() {

    $(window).scrollTop(0); // scroll to top here

    var _this = this;
    var $el = $(this.newContainer);

    $(this.oldContainer).hide();

    $el.css({
      visibility : 'visible',
      opacity : 0
    });

    $el.animate({ opacity: 1 }, 400, function() {
      /**
       * Do not forget to call .done() as soon your transition is finished!
       * .done() will automatically remove from the DOM the old Container
       */

      _this.done();
    });

As long as you put $(window).scrollTop(0); before the animate function you should be fine.