Boosting Frontend Speed: Quick Wins for Backend Developers

by Paul Conroy

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Boosting Frontend Speed: Quick Wins for Backend Developers Paul Conroy / @conroyp 21st June, 2024

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From Dublin, Ireland Started playing with the web 30+ years ago (Notepad, Frontpage & Geocities!) CTO at Square1 conroyp.com / @conroyp Paul Conroy 👴 🌍 🇮🇪

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In the beginning ● First website in 1991 ● Plain text, links - simple! https://info.cern.ch/hypertext/WWW/TheProject.html

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In the beginning ● First website in 1991 ● Plain text, links - simple! ● Img tag! Scrolling marquees! ● Basic CSS

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In the beginning ● First website in 1991 ● Plain text, links - simple! ● Img tag! Scrolling marquees! ● Basic CSS

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In the beginning ● First website in 1991 ● Plain text, links - simple! ● Img tag! Scrolling marquees! ● Basic CSS -> More advanced CSS ● Interactivity (Java applets, Flash, Javascript)

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Evolving ecosystem

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“The site is slow” - Your boss

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Improved metrics ● Stand-alone metrics ● Objectively quantify performance ● Core Web Vitals - how does the site “feel”? ● Google search algorithm ● CLS, LCP, INP

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Improved metrics ● CLS - how much do things jump around on a page? ● LCP - how long does it take to draw the biggest thing on the page? ● INP - how long between clicking and seeing something happen? (menu open etc)

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● Uses same data Google uses in rankings ● Based on real-world Chrome user data ● More than page speed! Sitemaps, crawl errors, inbound links ● Data has a lag of ~30 days https://search.google.com/search-console/ Search Console

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https://pagespeed.web.dev/ ● Aggregate score 1 - 100 Page Speed Insights

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https://pagespeed.web.dev/ ● Aggregate score 1 - 100 ● Separate score for individual CWV metrics ● Detailed information on reasons behind failing metrics Page Speed Insights

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● Aggregate score 1 - 100 ● Separate score for individual CWV metrics ● Detailed information on reasons behind failing metrics ● Lab and “real world” data ● Server cache of ~30 minutes https://pagespeed.web.dev/ Page Speed Insights

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● Runs locally in Chrome ● Same as Page Speed Insights ● Local conditions impact results (cookies, cache, etc) ● Potential for significant variations run-to-run Lighthouse

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● Runs locally in Chrome ● Same as Page Speed Insights ● Local conditions impact results (cookies, cache, etc) ● Potential for significant variations run-to-run ● Lighthouse-php Lighthouse

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Lighthouse-PHP https://spatie.be/docs/lighthouse-php/v1/introduction

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Lighthouse-PHP https://spatie.be/docs/lighthouse-php/v1/introduction

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Lighthouse-PHP Consider a “?noads=1” url toggle to get a “raw” result https://spatie.be/docs/lighthouse-php/v1/introduction 💡

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How exactly are we meant to improve a slow website?

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Option 1

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Option 1

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Option 1 ● Send the team snowboarding for 6 months ● Browsers and hardware will improve in that time ● Problem solved

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Option 1 ● Send the team snowboarding for 6 months ● Browsers and hardware will improve in that time ● Problem solved ● Might need an Option 2…

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4 Horsemen of the Slowpocalypse Images Ads Videos Fonts

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Get rid of them all!

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Improve page speed score?

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Improve page speed score ✅

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Improve page speed score ✅ 😎 🍹 🏖

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Images

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● Images make up roughly 60% of average page load ● More responsive sites → more image sizes being generated ● Particularly tricky to manage when handling user- generated content! IMAGES JS HTML CSS, FONTS

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Image sizing ● Stops the image from appearing too large

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Image sizing ● Stops the image from appearing too large ● Still requires a large image download

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● Stops the image from appearing too large ● File size is appropriate to the image being shown Image sizing ● Stops the image from appearing too large ● Still requires a large image download

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Choosing the right size ● Detecting the browser size based on User Agent / headers ● Generate different markup based on browser size

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Choosing the right size ● Detecting the browser size based on User Agent / headers ● Generate different markup based on browser size ● Impact on URL-based caching ● How does it handle device resizing after load?

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Responsive images ● srcset allows multiple sizes to be specified in markup ● Browser can determine best one to load ● A single URL cache works fine! ● Resizing of the browser? Right image size loaded ● Getting the sizes right can be fiddly (high density devices)

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Smaller images ● Webp - image format from Google ● 25 - 30% file size reduction, with minimal quality drop ● Conversion support in many PHP image libraries ● 15 years old, but widespread support only recently https://photutorial.com/image-format-comparison-statistics/

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Can I Use…? https://caniuse.com/?search=webp

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● Important to “reserve” space! ● Tell the browser how much space we’ll need ● Different sizes on different devices? Define heights in media queries for each breakpoint

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Impact on page speed

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Impact on page speed

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Lazy loading ● Only load assets when they are needed ● Potentially save a lot of bandwidth ● Load images just before they scroll into view

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Lazy loading ● Only load assets when they are needed ● Potentially save a lot of bandwidth ● Load images just before they scroll into view

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THEN ● Load polyfill library ● When image top is near viewport, swap data-src and src ● Scroll listener thrashed rendering thread! Polyfills

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THEN ● Load polyfill library ● When image top is near viewport, swap data-src and src ● Scroll listener thrashed rendering thread! Polyfills

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NOW ● loading=”lazy”, job done! 🔥 Polyfills

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https://caniuse.com/?search=loading="lazy"

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Lazyload everything?

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● Tempting to apply loading=”lazy” to all images ● Actively harmful if applied to images above the fold ● Browser is trying to optimise loading - help it out! Lazyload everything?

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Lazy loading background images ● Background images usually large, full width, lots of detail ● CSS property - background-image ● Some lazy loading polyfills support background images, some don’t!

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IntersectionObserver

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IntersectionObserver

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IntersectionObserver

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IntersectionObserver

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IntersectionObserver

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Display ads ● A developer has no way of knowing if an ad will show or not until the ad server responds ● Page content “jumping” - very bad for CLS ● Very annoying for users! ● Accidental clicks, maybe good for site owners?

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Two-click penalty ● Google adds overlay on ads, asks user to click again ● Unexpected behaviour! Most users won’t click again ● Google don’t tell you this is happening! ● It doesn’t show to every user ● How do we know when it’s happening?

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Avoiding the Two-click Penalty ● Label ads clearly ● Consistent spacing from content ● Avoid areas near menus, buttons, etc ● Prevention is better than cure!

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Reducing CLS ● Min-height on the ad container, matching expected ad unit size ● Same technique as with images

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● Min-height on the ad container, matching expected ad unit size ● Same technique as with images ● Ad loads in, taking the reserved space, no CLS or “Jumping” Reducing CLS

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● Min-height on the ad container, matching expected ad unit size ● Same technique as with images ● Ad loads in, taking the reserved space, no CLS or “Jumping” Reducing CLS

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Variable ad sizes? ● Responsive ad sizes (single request in markup) ● Google might give us more than we ask for! ● How do we reserve the right space for each ad when we don’t know the size?

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Callbacks ● Google Ad Manager has a slotRenderEnded callback ● When an ad loads, check what div it was in ● If ad is smaller than our min height, remove the min height

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Callbacks ● Set min height to that of most popular ad unit ● “Bakes in” some CLS, but should be net positive

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Results ● Users experiencing bad CLS fell by 64% overnight ● Regular review of most popular slots is critical

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4 Horsemen of the Slowpocalypse Images Ads Videos Fonts

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User Engagement & SEO benefits! ● Popular way to share content ● Strong user engagement ● Helps with SEO ● Easy embed options ● Hugely expensive payloads!

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How expensive are they really though?

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How expensive are they really though?

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How expensive are they really though?

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How expensive are they really though?

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A facade, you say… 🤔 How expensive are they really though?

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Web components Lite Youtube Embed by Paul Irish This component: ● Loads a placeholder image ● On hover warms the connection to youtube ● On click, swaps the image for the player code

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Web components Lite Youtube Embed by Paul Irish This component: ● Loads a placeholder image ● On hover warms the connection to youtube ● On click, swaps the image for the player code

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Web components Lite Youtube Embed by Paul Irish This component: ● Loads a placeholder image ● On hover warms the connection to youtube ● On click, swaps the image for the player code

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Performance impact?

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Performance impact?

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Performance impact?

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Performance impact?

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Performance impact? 🐢 🐰 ⚡⚡⚡

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SEO impact ● Google is good at recognising embedded videos! ● Doesn’t recognise components so well ● Use structured data alongside custom components ● VideoObject schema https://schema.org/VideoObject

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4 Horsemen of the Slowpocalypse Images Ads Videos Fonts

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Web fonts ● A key part of a dynamic, attractive web ● Brand “personality”, can brighten up dull sites ● Customisation comes at a cost!

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● Wide browser support ● Copied through the ages! ● Do we still need it all?

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https://caniuse.com/?search=woff2

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● Wide browser support ● Copied through the ages! ● Do we still need it all?

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● Wide browser support ● Copied through the ages! ● Do we still need it all?

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● woff2 is all we need ● Trim the markup ● Delete extra font files

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What is a font?

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Font subsetting ● Removing all characters we won’t use ● Glyphhanger, install via npm or pip ● Convert to woff2 while we’re at it

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Font subsetting

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Before

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After From 403kb to 138kb - nearly a 65% reduction in file size!

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What happens if someone uses a character not in my font set? ● Browser tries all the fonts defined in the font stack, in order ● If the character is not found in any of them, fall back to the system font ● If the system font has nothing, a placeholder box or empty space will show

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● MS Outlook converts :) :| and :( into smileys via Wingdings ● Those Wingding character codes use the slots for J / K / L ● No Wingdings on your system? Fall back to J / K / L in the next available font

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Google Fonts Subset via URL: Specific characters only:

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Google Fonts Self-hosting Google Fonts - https://github.com/spatie/laravel-google-fonts Subset via URL: Specific characters only:

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● Faster fonts, unblock rendering thread sooner ● LCP is probably an image, but is in a queue ● It’s critical to understand the data points you are looking at! Is this data telling me what I think it is?

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Incidents By Driver

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● When dealing with image issues, have we other blocking resources? ● Improving font loading can unblock threads, allowing faster image loading ● Holistic view - top line metrics rarely influenced by solely one thing

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4 Horsemen of the Slowpocalypse Images Ads Videos Fonts

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What’s next?

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ADDY OSMANI ● Chrome engineering lead ● Web performance ● New browser features https://twitter.com/addyosmani RICK VISCOMI ● Web Perf DevRel at Chrome ● Optimisations for CWV ● CrUX report data  https://twitter.com/rick_viscomi WEB.DEV ● All aspects of web dev ● Sections focused on perf metrics  https://web.dev/ SPATIE ● Media Library ● Lighthouse PHP ● Self-host Google Fonts  https://spatie.be/

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Takeaways? Images ● Pre-sized correctly ● Reserve space in the markup ● Use native browser features, remove polyfills Fonts ● Subsetting with Glyphanger ● Avoid google fonts, self-host Ads ● Reserve space (avoid CLS) ● Avoid 2-click penalty! Labelling and positioning Videos ● Use facades ● SEO impact! Structured data

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Conroyp.com   @conroyp   [email protected] Thank you! 🌍 🌐 📧