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larlet-fr-david-cache


			
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<h1>
  <span><a id="jumper" href="#jumpto" title="Un peu perdu ?">?</a></span>
  Cache-limiting in Service Workers (archive)
  <time>Pour la pérennité des contenus liés. Non-indexé, retrait sur simple email.</time>
</h1>
<section>
  <article>
    <h3><a href="https://adactio.com/journal/9844">Source originale du contenu</a></h3>
    <p>When I was documenting <a href="https://adactio.com/journal/9775">my first Service Worker</a> I mentioned that every time a user requests a page, I store that page in a cache for later (offline) use:</p>

<blockquote>
  <p>Right now I’m stashing any HTML pages the user visits into the cache. I don’t think that will get out of control—I imagine most people only ever visit just a handful of pages on my site. But there’s the chance that the cache could get quite bloated. Ideally I’d have some way of keeping the cache nice and lean.</p>

  <p>I was thinking: maybe I should have a separate cache for HTML pages, and limit the number in that cache to, say, 20 or 30 items. Every time I push something new into that cache, I could pop the oldest item out.</p>

  <p>I could imagine doing something similar for images: keeping a cache of just the most recent 10 or 20.</p>
</blockquote>

<p>Well I&#8217;ve done that now. Here&#8217;s <a href="https://gist.github.com/adactio/4d588bb8a65fa11a3ea3">the updated Service Worker code</a>.</p>

<p>I&#8217;ve got a function in there called <code>stashInCache</code> that takes a few arguments: which cache to use, the maximum number of items that should be in there, the request (URL), and the response:</p>

<pre><code>var stashInCache = function(cacheName, maxItems, request, response) {
    caches.open(cacheName)
        .then(function (cache) {
            cache.keys()
                .then(function (keys) {
                    if (keys.length &lt; maxItems) {
                        cache.put(request, response);
                    } else {
                        cache.delete(keys[0])
                            .then(function() {
                                cache.put(request, response);
                            });
                    }
                })
        });
};
</code></pre>

<p>It looks to see if the current number of items in the cache is less than the specified maximum:</p>

<pre><code>if (keys.length &lt; maxItems)
</code></pre>

<p>If so, go ahead and cache the item:</p>

<pre><code>cache.put(request, response);
</code></pre>

<p>Otherwise, delete the first item from the cache and <em>then</em> put the item in the cache:</p>

<pre><code>cache.delete(keys[0])
  .then(function() {
    cache.put(request, response);
  });
</code></pre>

<p>For HTML requests, I limit the cache to 35 items:</p>

<pre><code>var copy = response.clone();
var cacheName = version + pagesCacheName;
var maxItems = 35;
stashInCache(cacheName, maxItems, request, copy);
return response;
</code></pre>

<p>For images, I&#8217;m limiting the cache to 20 items:</p>

<pre><code>var copy = response.clone();
var cacheName = version + imagesCacheName;
var maxItems = 20;
stashInCache(cacheName, maxItems, request, copy);
return response;
</code></pre>

<p>Here&#8217;s <a href="https://adactio.com/serviceworker.js">my updated Service Worker</a>.</p>

<p>The cache-limited seems to be working for pages. But for some reason the images cache has blown past its allotted maximum of 20 (you can see the items in the caches under the &#8220;Resources&#8221; tab in Chrome under &#8220;Cache Storage&#8221;).</p>

<p>This is almost certainly because I&#8217;m doing something wrong or have completely misunderstood how the caching works. If you can spot what I&#8217;m doing wrong, <a href="https://adactio.com/contact">please let me know</a>.</p>
  </article>
</section>


<nav id="jumpto">
  <p>
    <a href="/david/blog/">Accueil du blog</a> |
    <a href="https://adactio.com/journal/9844">Source originale</a> |
    <a href="/david/stream/2019/">Accueil du flux</a>
  </p>
</nav>

<footer>
  <div>
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    <p>
      Bonjour/Hi!
      Je suis <a href="/david/" title="Profil public">David&nbsp;Larlet</a>, je vis actuellement à Montréal et j’alimente cet espace depuis 15 ans. <br>
      Si tu as apprécié cette lecture, n’hésite pas à poursuivre ton exploration. Par exemple via les <a href="/david/blog/" title="Expériences bienveillantes">réflexions bimestrielles</a>, la <a href="/david/stream/2019/" title="Pensées (dés)articulées">veille hebdomadaire</a> ou en t’abonnant au <a href="/david/log/" title="S’abonner aux publications via RSS">flux RSS</a> (<a href="/david/blog/2019/flux-rss/" title="Tiens c’est quoi un flux RSS ?">so 2005</a>).
    </p>
    <p>
      Je m’intéresse à la place que je peux avoir dans ce monde. En tant qu’humain, en tant que membre d’une famille et en tant qu’associé d’une coopérative. De temps en temps, je fais aussi des <a href="https://github.com/davidbgk" title="Principalement sur Github mais aussi ailleurs">trucs techniques</a>. Et encore plus rarement, <a href="/david/talks/" title="En ce moment je laisse plutôt la place aux autres">j’en parle</a>.
    </p>
    
    <p>
      Voici quelques articles choisis :
      <a href="/david/blog/2019/faire-equipe/" title="Accéder à l’article complet">Faire équipe</a>,
      <a href="/david/blog/2018/bivouac-automnal/" title="Accéder à l’article complet">Bivouac automnal</a>,
      <a href="/david/blog/2018/commodite-effondrement/" title="Accéder à l’article complet">Commodité et effondrement</a>,
      <a href="/david/blog/2017/donnees-communs/" title="Accéder à l’article complet">Des données aux communs</a>,
      <a href="/david/blog/2016/accompagner-enfant/" title="Accéder à l’article complet">Accompagner un enfant</a>,
      <a href="/david/blog/2016/senior-developer/" title="Accéder à l’article complet">Senior developer</a>,
      <a href="/david/blog/2016/illusion-sociale/" title="Accéder à l’article complet">L’illusion sociale</a>,
      <a href="/david/blog/2016/instantane-scopyleft/" title="Accéder à l’article complet">Instantané Scopyleft</a>,
      <a href="/david/blog/2016/enseigner-web/" title="Accéder à l’article complet">Enseigner le Web</a>,
      <a href="/david/blog/2016/simplicite-defaut/" title="Accéder à l’article complet">Simplicité par défaut</a>,
      <a href="/david/blog/2016/minimalisme-esthetique/" title="Accéder à l’article complet">Minimalisme et esthétique</a>,
      <a href="/david/blog/2014/un-web-omni-present/" title="Accéder à l’article complet">Un web omni-présent</a>,
      <a href="/david/blog/2014/manifeste-developpeur/" title="Accéder à l’article complet">Manifeste de développeur</a>,
      <a href="/david/blog/2013/confort-convivialite/" title="Accéder à l’article complet">Confort et convivialité</a>,
      <a href="/david/blog/2013/testament-numerique/" title="Accéder à l’article complet">Testament numérique</a>,
      et <a href="/david/blog/" title="Accéder aux archives">bien d’autres…</a>
    </p>
    <p>
      On peut <a href="mailto:david%40larlet.fr" title="Envoyer un courriel">échanger par courriel</a>. Si éventuellement tu souhaites que l’on travaille ensemble, tu devrais commencer par consulter le <a href="http://larlet.com">profil dédié à mon activité professionnelle</a> et/ou contacter directement <a href="http://scopyleft.fr/">scopyleft</a>, la <abbr title="Société coopérative et participative">SCOP</abbr> dont je fais partie depuis six ans. Je recommande au préalable de lire <a href="/david/blog/2018/cout-site/" title="Attention ce qui va suivre peut vous choquer">combien coûte un site</a> et pourquoi je suis plutôt favorable à une <a href="/david/pro/devis/" title="Discutons-en !">non-demande de devis</a>.
    </p>
    <p>
      Je ne traque pas ta navigation mais mon
      <abbr title="Alwaysdata, 62 rue Tiquetonne 75002 Paris, +33.184162340">hébergeur</abbr>
      conserve des logs d’accès.
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