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                <article class="panels-wrapper">
  <div class="panels">
     <section class="panel">
       <p>Fusce dapibus, tellus ac cursus commodo, tortor mauris condimentum nibh, ut fermentum massa justo sit amet risus. Nullam quis risus eget urna mollis ornare vel eu leo.</p>
     <section class="panel">
       <p>Maecenas sed diam eget risus varius blandit sit amet non magna. Integer posuere erat a ante venenatis dapibus posuere velit aliquet.</p>
     <section class="panel">
       <p>Nullam quis risus eget urna mollis ornare vel eu leo. Integer posuere erat a ante venenatis dapibus posuere velit aliquet.</p>
  <nav class="panels-nav">
    <button class="panels-nav-btn panels-nav-prev">&larr;</button>
    <ul class="panels-nav-menu">
      <li class="panels-nav-menu-item">&bull;</li>
      <li class="panels-nav-menu-item">&bull;</li>
      <li class="panels-nav-menu-item">&bull;</li>
    <button class="panels-nav-btn panels-nav-next">&rarr;</button>


                // THE IMPORTANT BITS:
// ------------------

$panel-width: 400px;

// The wrapper has to have a width set, and it should have
// overflow:hidden set to hide everything but the current slide:
.panels-wrapper {
  width: $panel-width;
  overflow-x: hidden;
  // overflow-x: visible; // leave visible for debugging

// The inner wrapper has display:flex to allow the items to sit side-by side
// and take up the same vertical space. No width is set - this is calculated in
// the JS. The transforamtion is also done in the JS. ANimations can be
// added here through.
.panels {
  display: flex;
  transition: all .275s ease-out;

// This needs the same width as the outer container, so that the panels
// fit exactly.
.panel {
  // problems with padding/box-sizing unless I explicitly specify this:
  flex-basis: $panel-width;

// -------------

$amethyst: #9b59b6; // light purple
$wisteria: #8e44ad; // purple
$clouds: #ecf0f1; // light grey
$silver: #bdc3c7; // grey
$westasphalt: #34495e; // lighter blue-grey
$midnightblue: #2c3e50;  // blue-grey

$panel-bg: $clouds;
$panel-text-color: $westasphalt;

$nav-bg: $amethyst;
$nav-btn-color: $midnightblue;

body {
  width: 100vw;
  min-height: 100vh;
  overflow-x: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;

.panels-wrapper {
  background-color: $panel-bg;
  color: $panel-text-color;
  font-weight: 300;

.panel {
  padding: 1rem;

.panels-nav {
  background-color: $nav-bg;
  display: flex;
  justify-content: space-between;
  align-items: center;

.panels-nav-btn {
  background: transparent;
  border: 0;
  box-shadow: 0;
  color: $nav-btn-color;
  font-size: 2rem;
  &:focus, &:active, &:hover {
    color: darken($nav-btn-color, 20%);

.panels-nav-btn.disabled, {
  pointer-events: none;
  opacity: 0.25;

.panels-nav-menu {
  display: flex;

.panels-nav-menu-item {
  color: $nav-btn-color;
  cursor: pointer;
  margin: .25rem;


                function SliderCore({
  slideContainerSelector = '[data-panels-id]',
  slideControlSelector = '[data-panel-control]'
}) {
  const slides = document.querySelector

function nextable() {}
function previousable() {}
function conditionallyNextable() {}
function conditionallyPreviousable() {}
function jumptoable() {}
function slidable() {}
function swipeable() {}
function autoplayable() {}

// This is fairly primitive, but it works well enough.
// With this being a class, I can create any number of sliders on
// a page by using `new Slider(options)`.
// FIXME: this is not possible at the minute, because I'm selecting
// on a `document` basis; needs to be scoped to the outer selector.
class Slider {
  // The constructor takes a selector for the element that contains the
  // panels, and the next/prev nav buttons.
  // The selectors are defined in an object, like:
  //    {
  //      panelsSelector: `.panels`,
  //      prevBtnSelector: `.panels-nav-prev`,
  //      nextBtnSelector: `.panels-nav-next`
  //    }
  constructor({ panelsSelector, prevBtnSelector, nextBtnSelector, panelNavSelector = null }) {
    // In the constructor, I take the selectors, and turn them into actual
    // references to elements in the document.
    this.panelsContainer = document.querySelector(panelsSelector);
    // I don't need to search for the individual panels - I just grab the children
    // of their container.
    this.panels = this.panelsContainer.children;
    // I could have simplified this further by just selecting
    // the block with the buttons in and using `.children` again,
    // but I want to be able to individually enable/disable them.
    this.prevBtn = document.querySelector(prevBtnSelector);
    this.nextBtn = document.querySelector(nextBtnSelector);
    // I want a set of nav items so if necessary I can select
    // a specific panel.
    this.panelNav = document.querySelector(panelNavSelector);
    this.panelNavItems = Array.from(this.panelNav.children);
    // Instead of keeping references in the dom, I keep a record
    // of whereabout the slider is at in a state object. This is
    // similar to how React deals with things:
    this.state = {
      currentPanelIndex: 0,
      firstPanelIndex: 0,
      lastPanelIndex: this.panels.length - 1
  // If I'm on the last panel, I can't logically go further right. And
  // if I'm on the first panel, I can't go further left. I'll just disble
  // the buttons if that's the case.
  enableDisableButtons() {
    if(this.state.currentPanelIndex === this.state.firstPanelIndex) { this.prevBtn.classList.add(`disabled`); } else { this.prevBtn.classList.remove(`disabled`); }
    if(this.state.currentPanelIndex === this.state.lastPanelIndex) { this.nextBtn.classList.add(`disabled`); } else { this.nextBtn.classList.remove(`disabled`); }
  // The next/previous handlers do three things:
  // As long as it isn't the lest/first panel (when they do nothing), they:
  // 1. change the `currentPanelIndex` in the state by +/- 1
  // 2. use a CSS translate to slide the whole slide container horizontally
  // 3. Enable or disable the next/prev button if necessary.
  nextPanelHandler() {
    if (this.state.currentPanelIndex < this.state.lastPanelIndex) {
      this.state.currentPanelIndex += 1;
  prevPanelHandler() {
    if (this.state.currentPanelIndex > this.state.firstPanelIndex) {
      this.state.currentPanelIndex -= 1;
  gotoPanelHandler(e) {
    console.log(`current index: ${this.state.currentPanelIndex}, target index: ${this.panelNavItems.indexOf(e.currentTarget)}`);
    if (this.state.currentPanelIndex !== this.panelNavItems.indexOf(e.currentTarget)) {
      this.state.currentPanelIndex = this.panelNavItems.indexOf(e.currentTarget);
  // By translating horizontally by a % of the total width, the slide is acheived.
  // So, for example, say there are 3 slides. The container for the slides is
  // 300% of the width of the parent. If the slider goes to the first
  // slide (at index 0), then the calculation is -(0 * 100 / 3), or -0.
  // If the slider goes to the third slide (at index 2), then the calculation
  // is -(2 * 100 / 3), or -66.6%. The slide container will move 66.6% of it's total
  // width to the left, which will bring the last slide fully into view.
  slideHorizontal() { = `translateX(-${(this.state.currentPanelIndex * 100) / this.panels.length}%)`;
  // The init function triggers the slider.
  init() {
    // Set the width of the panels container to panels.lenth * 100% of the parent, to allow it to slide. = `${this.panels.length * 100}%`;
    // The slider always starts on the first item. 
    // Add an index data attribute to all the nav items, and make the first item active.
    // FIXME Hacky, adding event handler to each item for the minute
    // this.panelNavItems.forEach(navItem => addEventListener('click', this.gotoPanelHandler.bind(this), true));
    this.prevBtn.addEventListener('click', this.prevPanelHandler.bind(this), true);
    this.nextBtn.addEventListener('click', this.nextPanelHandler.bind(this), true);

const mySlider = new Slider({panelsSelector: `.panels`, prevBtnSelector: `.panels-nav-prev`, nextBtnSelector: `.panels-nav-next`, panelNavSelector: `.panels-nav-menu`});