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                <p class="instructions">Pick the cities in the order you would wish to visit.</p>

<div id="app">
  <div class="container">
    <!-- create our empty "backing" that our choices will slide into, technically on top -->
    <ul class="list-back">
      <li v-for="city in cities" :key="city"></li>
    <!-- transition-group works the much the same as transition, but for "lists" -->
    <!-- note the tag attribute states "ul", otherwise it defaults to span -->
    <transition-group :name="currentListTransition" tag="ul" class="list">
      <!-- whenever a choice is made, for loop updates the markup -->
      <li v-for="(item, index) in selectedItems" :key="item">{{ item }}</li>
  <div class="container">
    <ul class="list">
      <!-- creates our list to choose from -->
      <li class="city" v-for="(city, index) in cities" :key="city" :data-index="index" @click="chooseCity">{{ city }}</li>
  <div class="panel">
    <!-- this appears to be the button to clear our selected list -->
    <button class="clear" @click="clearSelection">clear</button>



                body {
  background-color: #707070;
  font-family: sans-serif;
  height: 100vh;
  overflow: hidden;
  width: 100vw;

#app {
  align-items: center;
  display: flex;
  flex-wrap: wrap;
  height: 100%;
  justify-content: center;
  width: 100%;

.instructions {
  color: white;
  font-size: 20px;
  text-align: center;

.container {
  height: 150px;
  margin: 20px;
  position: relative;
  width: 200px;

.list-back {
  align-items: center;
  bottom: 0;
  display: flex;
  flex-direction: column;
  justify-content: flex-start;
  left: 0;
  margin: auto;
  position: absolute;
  right: 0;
  top: 0;
  li {
    align-items: center;
    display: flex;
    flex-shrink: 0;
    font-size: 24px;
    height: 34px;
    justify-content: center;
    margin-bottom: 4px;
    width: 100%;
.list-back li {
  background-color: #E0E0E0;
  border-radius: 24px;

.city {
  background-color: #E0E0E0;
  border-radius: 24px;
  cursor: pointer;
  transition: 0.5s;
  &:hover {
    background-color: #307B21;
    color: #F5F5F5;
  &.selected {
    opacity: 0.5;
    pointer-events: none;
.panel {
  display: flex;
  justify-content: center;
  width: 100%;
  .clear {
    background-color: #C11826;
    border: {
      radius: 8px;
      style: none;
    color: #F5F5F5;
    cursor: pointer;
    padding: 8px 16px;

// each transition is prefixed with the direction they are to appear from
.top-enter-active, .top-leave-active { transition: 0.5s; }
.top-enter, .top-leave-to { opacity: 0; transform: translate3d(0, -40px, 0); }
.top-move { opacity: 0.5; transition: 0.5s; }

.left-enter-active, .left-leave-active { transition: 0.5s; }
.left-enter, .left-leave-to { opacity: 0; transform: translate3d(-40px, 0, 0); }
.left-move { opacity: 0.5; transition: 0.5s; }

// this transition is also used from the "clear" button
.right-enter-active, .right-leave-active { transition: 0.5s; }
.right-enter, .right-leave-to { opacity: 0; transform: translate3d(40px, 0, 0); }
.right-move { opacity: 0.5; transition: 0.5s; }

.bottom-enter-active, .bottom-leave-active { transition: 0.5s; }
.bottom-enter, .bottom-leave-to { opacity: 0; transform: translate3d(0, 30px, 0); }
.bottom-move { opacity: 0.5; transition: 0.5s; }

// if animations are reduced at the OS level, turn off transitions
@media screen and (prefers-reduced-motion: reduce) {
  .top-enter-active, .top-leave-active { transition: none; }
  .top-move { transition: none; }
  .left-enter-active, .left-leave-active { transition: none; }
  .left-move { transition: none; }
  .right-enter-active, .right-leave-active { transition: none; }
  .right-move { transition: none; }
  .bottom-enter-active, .bottom-leave-active { transition: none; }
  .bottom-move { transition: none; }


                new Vue({
  el: "#app",
  data: {
    // array to keep track of selected cities
    selectedItems: [],
    // array of the current choices
    cities: ['Chicago', 'New York', 'Seattle', 'Miami', 'Boston'],
    // this string gets changed as choices are made
    // but we know the first one will be from the top anyway...
    currentListTransition: 'top'
  methods: {
    // method for the city list you choose from
    // the index is passed because that easily relates to the arrays
  	chooseCity: function (event) {
      let selectedLength = this.selectedItems.length;
      let citiesLength = this.cities.length;
      let clt = this.currentListTransition;
      // somewhat complicated if/else sequence
      // mainly because I wanted left and right entries for the middle items
      if (selectedLength === 0) {
        // we most likely don't require this since it is default
        // but, you never know
        clt = 'top';
      } else if (selectedLength > 0 && selectedLength < citiesLength - 1) {
        // check the previous transition direction
        // if it was top or left then go right, if it was right then go left
        // could reverse this, or even make it random for a large list
      	clt = clt === 'top' || clt === 'left' ? 'right' : 'left';
      } else if (selectedLength === citiesLength - 1) {
        // always make last one appear from bottom
        clt = 'bottom';
      // update the transition
    	this.currentListTransition = clt;
      // push the choice into the array to trigger the transition
      // mark the choice as selected'selected');
    clearSelection: function () {
      // make everything disappear to the right
      // this can be changed to any of the other transitions
    	this.currentListTransition = 'right';
      // clearing the array causes chosen cities to go transition out
    	this.selectedItems = [];
      // clear selections so we can start again
      document.querySelectorAll('.city.selected').forEach(element => {