mContext.github.io/js/bookmark.js

/* global CONFIG */

window.addEventListener('DOMContentLoaded', () => {
  'use strict';

  var doSaveScroll = () => {
    localStorage.setItem('bookmark' + location.pathname, window.scrollY);
  };

  var scrollToMark = () => {
    var top = localStorage.getItem('bookmark' + location.pathname);
    top = parseInt(top, 10);
    // If the page opens with a specific hash, just jump out
    if (!isNaN(top) && location.hash === '') {
      // Auto scroll to the position
      window.anime({
        targets  : [document.documentElement, document.body],
        duration : 200,
        easing   : 'linear',
        scrollTop: top
      });
    }
  };
  // Register everything
  var init = function(trigger) {
    // Create a link element
    var link = document.querySelector('.book-mark-link');
    // Scroll event
    window.addEventListener('scroll', () => link.classList.toggle('book-mark-link-fixed', window.scrollY === 0));
    // Register beforeunload event when the trigger is auto
    if (trigger === 'auto') {
      // Register beforeunload event
      window.addEventListener('beforeunload', doSaveScroll);
      window.addEventListener('pjax:send', doSaveScroll);
    }
    // Save the position by clicking the icon
    link.addEventListener('click', () => {
      doSaveScroll();
      window.anime({
        targets : link,
        duration: 200,
        easing  : 'linear',
        top     : -30,
        complete: () => {
          setTimeout(() => {
            link.style.top = '';
          }, 400);
        }
      });
    });
    scrollToMark();
    window.addEventListener('pjax:success', scrollToMark);
  };

  init(CONFIG.bookmark.save);
});