pinafore/routes/_components/NavItem.html

<a class='main-nav-link {selected ? "selected" : ""}'
   aria-label={ariaLabel}
   aria-current={selected}
   on:click="onClick(event)"
   {href} >
  <div class="nav-icon-and-label">
    {#if name === 'notifications'}
    <div class="nav-link-svg-wrapper">
      <svg class="nav-link-svg">
        <use xlink:href={svg} />
      </svg>
      {#if $hasNotifications}
      <span class="nav-link-notifications" aria-hidden="true">
          {$numberOfNotifications}
        </span>
      {/if}
    </div>
    {:else}
    <svg class="nav-link-svg">
      <use xlink:href={svg} />
    </svg>
    {/if}
    <span class="nav-link-label">{label}</span>
  </div>
  <div class="nav-indicator"
       nav-indicator-key={name}
       ref:indicator
  ></div>
</a>
<style>
  .main-nav-link {
    text-decoration: none;
    display: flex;
    justify-content: center;
    align-items: center;
    flex: 1;
    flex-direction: column;
  }

  .nav-icon-and-label {
    padding: 15px 20px;
    display: flex;
    justify-content: center;
    align-items: center;
    flex: 1;
  }

  .nav-link-svg-wrapper {
    position: relative;
    display: inline-block;
  }

  .nav-link-svg-wrapper, .nav-link-svg {
    width: 20px;
    height: 20px;
  }

  .nav-link-notifications {
    position: absolute;
    display: flex;
    align-items: center;
    justify-content: center;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    transform: translate(10px, 7px);
    z-index: 10;
    border: 1px solid var(--nav-bg);
    background: var(--nav-svg-fill);
    color: var(--nav-bg);
    border-radius: 100%;
    font-size: 0.9em;
    margin: 3px 0;
  }

  .main-nav-link.selected {
    background: var(--nav-a-selected-bg);
  }

  .main-nav-link.selected:hover {
    background: var(--nav-a-selected-bg-hover);
  }

  .nav-indicator {
    width: 100%;
    height: 1px;
    background: var(--nav-a-border);
    transform-origin: left;
  }

  .nav-indicator.animate {
    transition: transform 333ms ease-in-out;
  }

  .main-nav-link:hover .nav-indicator {
    background: var(--nav-a-border-hover);
  }

  .main-nav-link.selected .nav-indicator {
    background: var(--nav-a-selected-border);
  }

  .main-nav-link.selected:hover .nav-indicator {
    background: var(--nav-a-selected-border-hover);
  }

  .main-nav-link:hover {
    background-color: var(--nav-a-bg-hover);
    text-decoration: none;
  }

  .main-nav-link:hover .nav-link-label {
    color: var(--nav-text-color-hover);
  }
  .main-nav-link:hover .nav-link-svg {
    fill: var(--nav-svg-fill-hover);
  }

  .nav-link-svg {
    display: inline-block;
    fill: var(--nav-svg-fill);
  }

  .nav-link-label {
    font-size: 16px;
    color: var(--nav-text-color);
    padding-left: 10px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
  }

  @media (max-width: 991px) {
    .main-nav-link .nav-link-label {
      display: none;
    }
    .nav-link-svg-wrapper, .nav-link-svg {
      width: 25px;
      height: 25px;
    }
    .nav-icon-and-label {
      padding: 20px 0;
    }
    .nav-link-notifications {
      transform: translate(15px, 7px);
      margin: 3px 1px 4px;
    }
  }
</style>
<script>
  import { store } from '../_store/store'
  import { smoothScrollToTop } from '../_utils/smoothScrollToTop'
  import { on, emit } from '../_utils/eventBus'
  import { mark, stop } from '../_utils/marks'
  import { doubleRAF } from '../_utils/doubleRAF'

  export default {
    oncreate () {
      let { name } = this.get()
      let indicator = this.refs.indicator
      on('animateNavPart1', this, ({fromPage, toPage}) => {
        if (fromPage !== name) {
          return
        }
        mark('animateNavPart1 gBCR')
        let fromRect = indicator.getBoundingClientRect()
        stop('animateNavPart1 gBCR')
        emit('animateNavPart2', {fromRect, fromPage, toPage})
      })
      on('animateNavPart2', this, ({fromPage, fromRect, toPage}) => {
        if (toPage !== name) {
          return
        }
        mark('animateNavPart2 gBCR')
        let toRect = indicator.getBoundingClientRect()
        stop('animateNavPart2 gBCR')
        let translateX = fromRect.left - toRect.left
        let scaleX = fromRect.width / toRect.width
        indicator.style.transform = `translateX(${translateX}px) scaleX(${scaleX})`
        let onTransitionEnd = () => {
          indicator.removeEventListener('transitionend', onTransitionEnd)
          indicator.classList.remove('animate')
        }
        indicator.addEventListener('transitionend', onTransitionEnd)
        doubleRAF(() => {
          indicator.classList.add('animate')
          indicator.style.transform = ''
        })
      })
    },
    store: () => store,
    computed: {
      selected: ({ page, name }) => page === name,
      ariaLabel: ({ selected, name, label, $numberOfNotifications }) => {
        let res = label
        if (selected) {
          res += ' (current page)'
        }
        if (name === 'notifications' && $numberOfNotifications) {
          res += ` (${$numberOfNotifications})`
        }
        return res
      }
    },
    methods: {
      onClick (e) {
        let { selected } = this.get()
        if (!selected) {
          return
        }
        e.preventDefault()
        e.stopPropagation()
        smoothScrollToTop(document.getElementsByClassName('container')[0])
      }
    }
  }
</script>