some js that I would like to make into something wonderful.

some.js

$(function () {

    function parallax(elm, move) {
        window.addEventListener('scroll', function(){
            var win_offset = window.pageYOffset;
            var bg_scroll = document.querySelectorAll(elm);
            var bg_scroll_len = bg_scroll.length;
            var parallax = win_offset / parseFloat('1.' + move);
            for (var i = bg_scroll_len - 1; i >= 0; i--) {
                bg_scroll[i].style.backgroundPosition = '0 -' + parallax + 'px';
            }
        });
    }

    function pushHash(hash) {
        if(history.pushState) {
            history.pushState(null, null, '#' + hash);
        } else {
            location.hash = hash;
        }
    }

    function scrollToHash(anchorID) {
        var anchorPos = $('#' + anchorID).offset();
        $('html, body').animate({scrollTop: anchorPos.top}, 400, function () {
            pushHash(anchorID);
        });
    }

    function changeChapter(direction) {
        var hash = location.hash.slice(1);
        var $hash_id = $('#' + hash);
        if(direction === 'next') {
            if ($hash_id.next().attr('id')) {
                scrollToHash($hash_id.next().attr('id'));
            }
        } else {
            if ($hash_id.prev().attr('id')) {
                scrollToHash($hash_id.prev().attr('id'));
            }
        }
    }

    $(window).on('scroll', function(e){
        e.preventDefault();
        var win_scroll_top = $(window).scrollTop();
        $('.js-chapters').each(function() {
            var $this = $(this);
            var elm_id = $this.attr('id');
            var elm_pos = $this.position().top;
            var elm_height = $this.height();
            if (elm_pos <= win_scroll_top && (elm_height + elm_pos) > win_scroll_top) {
                pushHash(elm_id);
            }
        });
    });

    // TODO: IE9 fallback with http://andreruffert.github.io/rangeslider.js/
    $('.js-font_slider').on('change', function (){
        var font_size = $(this).val();
        $('.js-report_interpretation_wrapper').css('font-size', font_size + 'px');
    });

    $('.js-arrow_up').on('click', changeChapter.bind(this, 'prev'));

    $('.js-arrow_down').on('click', changeChapter.bind(this, 'next'));

    $('a[href^="#"]').on('click', function (e) {
        e.preventDefault();
        scrollToHash($(this).attr('href').slice(1));
    });

    $('.js-table_of_contents').on('click', function (e){
        $(this).toggleClass('open');
        e.stopPropagation();
        $(document).one('click', function() {
            $('.js-table_of_contents').toggleClass('open');
        });
    });

    $('.js-more_options').on('click', function (e){
        $(this).toggleClass('open');
        e.stopPropagation();
        //$(document).one('click', function() {
        //    $('.js-more_options').toggleClass('open');
        //});
    });

    parallax('.js-parallax', 4);
});