Preloading, measured

// Hovering a link fetches its page and puts it in the cache before the click
const pagefold = new Pagefold({ plugins: [new PagefoldPreload()] })

const lines = document.querySelector('#lines')
const path = (url) => url.split('/').pop()
const log = (text, kind) => {
  const li = document.createElement('li')
  li.className = kind
  li.textContent = text
  lines.prepend(li)
}

// A page was fetched ahead of the click
pagefold.hooks.on('page:preload', (visit, { page }) => log(`preloaded ${path(page.url)}`, 'pre'))

// A visit: was the page already in the cache, and how long did it take to have it?
let started = 0
let cached = false
pagefold.hooks.on('visit:start', (visit) => {
  started = performance.now()
  cached = pagefold.cache.has(visit.to.url)
})
pagefold.hooks.on('page:load', (visit) => {
  const ms = Math.round(performance.now() - started)
  log(`opened ${path(visit.to.url)} · ${cached ? 'from the cache' : 'from the network'} · ${ms} ms`, cached ? 'hit' : 'miss')
})

// Forget everything, as you would after a login or a change of language
document.querySelector('#clear').addEventListener('click', () => {
  pagefold.cache.clear()
  log('cache emptied', 'pre')
})

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Home · Preload</title>
  <meta name="description" content="Hover first, then click">
  <link rel="stylesheet" href="../_lib/fade.css">
  <link rel="stylesheet" href="style.css">
</head>
<body>
  <header class="top">
    <strong>Preload</strong>
    <nav>
      <a href="index.html">Home</a>
      <a href="pricing.html">Pricing</a>
      <a href="docs.html">Docs</a>
      <a href="blog.html">Blog</a>
      <a href="team.html">Team</a>
    </nav>
  </header>
  <main id="pagefold" class="transition-fade">
    <h1>Home</h1>
    <p class="lead">Hover first, then click. Rest the pointer on a link for a moment and then click it.</p>
    <div class="tiles">
      <a class="tile" href="pricing.html"><b>Pricing</b><span>pricing.html</span></a>
      <a class="tile" href="docs.html"><b>Docs</b><span>docs.html</span></a>
      <a class="tile" href="blog.html"><b>Blog</b><span>blog.html</span></a>
      <a class="tile" href="team.html"><b>Team</b><span>team.html</span></a>
    </div>
  </main>
  <section id="log" aria-label="What Pagefold did">
    <header><b>Log</b><button type="button" id="clear">Empty the cache</button></header>
    <ol id="lines"></ol>
  </section>
  <script src="../_lib/pagefold.js"></script>
  <script src="../_lib/preload.js"></script>
  <script src="main.js"></script>
</body>
</html>

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html,body{min-height:100%}
body{margin:0;font:16px/1.6 system-ui,sans-serif;background:#0a0a0a;color:#fafaf8}
/* Links: the accent color with a quiet underline that gets stronger on hover */
a{color:#5af0ae;text-decoration:underline;text-decoration-thickness:1px;text-underline-offset:.25em;text-decoration-color:rgba(90,240,174,.5);transition:color .15s,text-decoration-color .15s}
a:hover{color:#00ff9c;text-decoration-color:currentColor}
a:focus-visible{outline:2px solid #5af0ae;outline-offset:3px;border-radius:2px}
.top{display:flex;align-items:center;justify-content:space-between;gap:1rem;padding:.8rem 1.5rem;border-bottom:1px solid #2c2c2c}
.top strong{font:700 .95rem ui-monospace,Menlo,monospace}
.top nav{display:flex;gap:1.25rem;flex-wrap:wrap}
main{padding:2rem 1.5rem 3rem;max-width:46rem}
h1{margin:0 0 .5rem;font-size:2.1rem;line-height:1.15}
p{margin:0 0 1rem;max-width:36rem;color:#c9c9c4}
.lead{color:#a3a39e;font-size:1.05rem}
.cards{display:grid;grid-template-columns:repeat(3,1fr);gap:.75rem;margin-top:1.5rem}
.card{border:1px solid #2c2c2c;background:#141414;border-radius:12px;padding:.9rem}
.card i{display:block;height:3.2rem;border-radius:8px;margin-bottom:.6rem}
.card b{display:block;font-size:.95rem}
.card span{font-size:.82rem;color:#a3a39e}
@media (max-width:34rem){.cards{grid-template-columns:1fr}main{padding:1.25rem}}
.tiles{display:grid;grid-template-columns:repeat(2,1fr);gap:.75rem;margin-top:1.25rem}
.tile{display:block;padding:1rem;border:1px solid #2c2c2c;border-radius:12px;background:#141414;color:#fafaf8;text-decoration:none}
.tile:hover{border-color:#00ff9c;background:#1a1a1a}
.tile b{display:block}
.tile span{font:.78rem ui-monospace,Menlo,monospace;color:#a3a39e}
main{padding-bottom:1rem}
#log{margin:0 1.5rem 1.5rem;border:1px solid #2c2c2c;border-radius:12px;background:#101010;max-width:46rem;font:.8rem ui-monospace,Menlo,monospace}
#log header{display:flex;justify-content:space-between;align-items:center;padding:.5rem .8rem;border-bottom:1px solid #2c2c2c}
#log button{font:inherit;color:#fafaf8;background:#1a1a1a;border:1px solid #2c2c2c;border-radius:8px;padding:.25rem .6rem;cursor:pointer}
#log button:hover{border-color:#00ff9c}
#lines{list-style:none;margin:0;padding:.4rem .8rem;max-height:9.5rem;overflow:auto}
#lines li{padding:.12rem 0;color:#a3a39e}
#lines .hit{color:#00ff9c}
#lines .miss{color:#ff9f5c}
#lines .pre{color:#7cc4ff}