In parts 1–3 we covered various ways that we optimized the loading patterns of the critical path static resources and data queries. However there is another key area we haven’t covered yet that’s crucial to improving web application performance, particularly on low-end devices — ship less code to the user — in particular, ship less JavaScript.

Since we’re already pushing data to the client at the earliest possible time in the page load — the only faster way to get data to the client would be to not have to fetch or push any data at all.

L’excès de JavaScript dégrade fortement l’expérience de navigation sur un site mobile, et je constate que personne ne pense à vérifier les performances sur tous les devices - encore moins ceux d’entrée de gamme. Pourtant ce sont les premiers à être bloqués si les JS ne sont pas optimisés
[…]
Les résultats de cette étude ont montré que, en dehors des 51 % de l'ensemble des visiteur.se.s qui disposent d’un iPhone ou d’un iPad, 30 % ont un smartphone d’entrée de gamme qui peut même être très vieux. C’est une part du trafic non négligeable pour qui l’expérience de navigation doit être la plus fluide possible !
<cite>Jean-Pierre Vincent</cite>

If you do find yourself in a position where your site’s initial rendering depends on a third-party script, refer to your mitigation plan to see what you can do to eliminate or ameliorate your dependence on it. Depending on a third party for core functionality is never a good position to be in, as you’re relinquishing a lot of control to others who might not have your best interests in mind.

Aussi, nous ne pouvons pas nous empêcher de supposer une volonté de Google de soulager son infrastructure.

Pourquoi vouloir à tout prix rendre un site rapide ? Pas seulement par souci UX ou par amour de son.a prochain.e, mais aussi parce que Google passe du temps à crawler un volume immense de pages.

The usual uses cases for Service Workers is pre-caching; custom offline pages; saving pages for offline reading. What if we could use the Push API to introduce a subscription strategy based on content push and offline first?

The crossorigin attribute, when used with rel="preconnect", doesn't describe where the target origin is but rather what kind of assets will be downloaded from that origin. If the assets use CORS, crossorigin is needed. If CORS won't be used, crossorigin should be omitted. If both types of assets will be present, two resource hints are necessary.

[…] Avant de vous lancer tête baissée dans une version AMP de votre site, pesez bien le pour et le contre, et assurez vous de savoir si cette démarche va réellement répondre à vos besoins pour réduire vos temps de chargement ; ou plutôt faire cautère sur jambe de bois en accélérant seulement certaines pages, et sur mobile uniquement.

Average cost, total impact and popularity of the main third parties.

The deep dive helped our team develop best practices that we are able to apply to our work going forward. It also helped us refine a performance mindset that encourages exploration. As we develop new features, we can apply what we’ve learned while always trying to improve on these techniques.

WebPageTest is an online tool and an Open Source project to help developers audit the performance of their websites. […] But things can get difficult pretty quickly when dealing with Single Page Applications […] How can you get through a log in page? How can you test the performance of your users’ flow, when most of it happens client-side and does not have a specific URL to point to?

How to keep up on web performance? The world of web development changes rapidly and measuring and optimizing performance is no exception. We are often presented with new tools, APIs and techniques for building websites that load fast.

A comprehensive and documented article on images on the web, their use and optimization.

Pour conclure, les 2 points à retenir à propos de Page Speed Insight qui est un bon outil, mais…

• des résultats sont à relativiser ;
• rien ne remplace l’œil et l’avis d’un.e expert.e pour savoir quelles optimisations appliquer et comment !

Pages Speed Insight propose ainsi un système de notation sévère qui pousse aux optimisations webperf - et c’est une bonne chose ! En effet, s’il ne faut pas le prendre au pied de la lettre (ou du chiffre), il invite malgré tout à réfléchir aux moyens d’améliorer ses temps de chargement.

So I often find myself looking at WebPageTest (WPT) waterfall charts, but as I seem to have the memory of a chimpanzee (not a goldfish, that’s a myth) I tend to forget some of the details and what they all mean. So I decided to pull together many bits of information into a single blog post I can then refer to at a later date.

Heart est un outil open-source et modulaire d’automatisation d’analyses de qualité web. Il met à contribution Mozilla Observatory, Qualys SSL Labs Server et Dareboost pour produire des rapports de qualité Web et les publier sur Slack.

Performance metrics are surprisingly challenging to get right.

Browsers don't always behave as we would want or expect them to, but we do have tools at our disposal to steer that behaviour towards the result we want.

Wikipedia reduceds the JS initial payload to fit within a budget of 28 KB. In total, the year-long effort is saving 4.3 Terabytes a day of bandwidth on our users' page views.