Simon Willison’s Weblog

Making GitHub’s new homepage fast and performant. A couple of really clever tricks in this article by Tobias Ahlin. The first is using IntersectionObserver in conjunction with the video preload=“none” attribute to lazily load a video when it scrolls into view. The second is an ingenious trick to create an efficiently encoded transparent JPEG image: embed the image in a SVG file twice, once as the image and once as a transparency mask. # 29th January 2021, 7:05 pm

Diffable: only download the deltas. JavaScript library for detecting and serving diffs to JavaScript rather than downloading large scripts every time a few lines of code are changed. “Using Diffable has reduced page load times in Google Maps by more than 1200 milliseconds (~25%). Note that this benefit only affects users that have an older version of the script in cache. For Google Maps that’s 20-25% of users.” # 11th July 2010, 12:19 pm

Lazy Load Plugin for jQuery. I’m using this jQuery plugin to save some bandwidth when people first view my Redis tutorial slides. It unobtrusively replaces images on a page with a placeholder graphic, then sets them to load automatically as the user scrolls down the page. # 26th April 2010, 12:02 am

Dojo 1.4.1 vs jQuery 1.4.2pre on Taskspeed. John Resig’s reponse. When JavaScript libraries compete on performance, everybody wins. # 29th January 2010, 2:19 pm

Dojo: Still Twice As Fast When It Matters Most. Alex Russell shows how Dojo out-performs jQuery on the TaskSpeed benchmark, which attempts to represent common tasks in real-world applications and has had code that have been optimised by the development teams behind each of the libraries. # 28th January 2010, 10:40 pm

jQuery 1.4 Alpha 1 Released. Impressively the new version contains no new features at all (correct me if I’m wrong), instead focusing on significant performance improvements to the existing API. # 5th December 2009, 5:31 pm

Google Analytics goes async. This is excellent news—the latest version of the Google Analytics JavaScript is designed to allow for asynchronous loading, so it won’t hold up the rendering of your page. Analytics and banner ads are the two worst offenders when it comes to slowing down page loads. Now if only a banner ad vendor would follow suit... # 2nd December 2009, 6:30 pm

LABjs: new hotness for script loading. Created in collaboration with Steve Souders, LABjs is a JavaScript loading library which makes it easy to have scripts download in parallel while still ensuring that they execute sequentially where required to ensure dependencies are met. It’s unclear how you would decide to use this over concatenating all scripts together in to a single file. # 26th November 2009, 12:28 pm

Gmail for Mobile: Reducing Startup Latency. Cheeky iPhone optimisation trick—parsing 200 KB of JavaScript takes an iPhone 2.2 device 2.6 seconds, so Gmail embeds code components in /* comments */ in a script tag and evals them on demand later on when the features are needed. # 23rd September 2009, 10:29 pm

Firefox 3.5 for developers. It’s out today, and the feature list is huge. Highlights include HTML 5 drag ’n’ drop, audio and video elements, offline resources, downloadable fonts, text-shadow, CSS transforms with -moz-transform, localStorage, geolocation, web workers, trackpad swipe events, native JSON, cross-site HTTP requests, text API for canvas, defer attribute for the script element and TraceMonkey for better JS performance! # 30th June 2009, 6:08 pm

Loading Scripts Without Blocking. Steve Souders is publishing extracts from his new book, “Even Faster Web Sites”. Here’s a systematic study of different JavaScript loading methods, along with a decision tree for picking the most appropriate one for your application. # 30th April 2009, 7:56 pm

Magic properties make Firefox synchronously load the Java plugin. Even defining a function called sun() (or several other symbols) will trigger the Java VM to be loaded, dramatically hurting the performance of your page. # 27th February 2009, 4:03 pm

jQuery 1.3.1 Released. Bug fix for 1.3, mainly browser compatibility issues. Of interest: jQuery no longer ship a packed version (where JS is used to further decompress a string), as their tests show that this reduces performance due to the overhead of the extra decompression. They still provide a YUI Compressor minified version. # 22nd January 2009, 10:41 am

Sloppy—the slow proxy. Java Web Start GUI application which runs a proxy to the site of your choice simulating lower connection speeds—great for testing how well your ajax holds up under poor network conditions. # 13th January 2009, 4:17 pm

Dromaeo: JavaScript Performance Testing (via) This is one classy benchmark. Run it in as many browsers as you like (each run is saved to the server and assigned a run ID), then compare the results by appending ?id=[run1],[run2]... to the URL. # 11th September 2008, 4:06 pm

TraceMonkey. Brendan Eich has been preaching the performance benefits of tracing and JIT for JavaScript on the conference circuit for at least a year, and the results from the first effort to be merged in to Mozilla core are indeed pretty astounding. # 22nd August 2008, 11:13 pm

SquirrelFish. WebKit’s JavaScript engine was no slouch, but that hasn’t stopped them from replacing it with a brand new “register-based, direct-threaded, high-level bytecode engine, with a sliding register window calling convention”. It runs 1.6x faster and has the Best Logo Ever. # 3rd June 2008, 7:57 am

20,000 Reasons Why Comet Scales. Greg Wilkins coaxes Jetty and Bayeux in to supporting 20,000 simultaneous users per server while maintaining sub-second latency, using Amazon EC2 to run the benchmark. # 7th January 2008, 8:32 am

Yahoo! Search Contextual Precaching. Neat performance trick on Yahoo! Search: the moment you start typing (indicating you intend to search) the site quietly fires off a bunch of requests to precache assets needed for the search results page. # 16th November 2007, 3:58 pm

Return of the HTTP overhead delay. Christian proposes a neat way of improving page performance, by delaying non-essential images such as avatars until after the rest of the page has loaded. # 11th July 2007, 3:12 pm

Reducing HTTP requests using make. Nice simple recipe for concatenating JavaScript in to one file using make—doesn’t do anything for cache-busting though. # 27th May 2007, 11:29 pm