Simon Willison’s Weblog

servefolder.dev (via) Absurdly clever application of service workers and the file system API: you can select a folder from your computer and the contents of that folder will be served (just to you) from a path on this website—all without uploading any content. The code is on GitHub and offers a useful, succinct introduction to how to use those APIs. # 12th December 2021, 6:32 pm

Deno Deploy Beta 3 (via) I missed Deno Deploy when it first came out back in June: it’s a really interesting new hosting environment for scripts written in Deno, Node.js creator Ryan Dahl’s re-imagining of Node.js. Deno Deploy runs your code using v8 isolates running in 28 regions worldwide, with a clever BroadcastChannel mechanism (inspired by the browser API of the same name) that allows instances of the server-side code running in different regions to send each other messages. See the “via” link for my annotated version of a demo by Ondřej Žára that got me excited about what it can do. # 7th November 2021, 1:51 am

Tonic (via) Really interesting library for building Web Components: it’s tiny (just 350 lines of code), works directly in browsers without any compile or build step and makes very creative use of modern JavaScript features such as async generators. # 23rd October 2021, 5:21 am

How to win at CORS (via) Jake Archibald’s definitive guide to CORS, including a handy CORS playground interactive tool. Also includes a useful history explaining why we need CORS in the first place. # 12th October 2021, 2:07 pm

Introducing Partytown 🎉: Run Third-Party Scripts From a Web Worker (via) This is just spectacularly clever. Partytown is a 6KB JavaScript library that helps you move gnarly poorly performing third-party scripts out of your main page and into a web worker, so they won’t destroy your page performance. The really clever bit is in how it provides sandboxed access to the page DOM: it uses a devious trick where a proxy object provides getters and setters which then make blocking API calls to a separate service worker, using the mostly-forgotten xhr.open(..., false) parameter that turns off the async default for an XMLHttpRequest call. # 23rd September 2021, 6:29 pm

Temporal: getting started with JavaScript’s new date time API. Axel Rauschmayer explores the new proposed API for handling dates, times and timezones in JavaScript., which is under development by Ecma TC39 at the moment (and made available as a Polyfill which you are recommended not to run in production since the API is still being figured out). This is a notoriously difficult problem so it’s always interesting to see the latest thinking on how to best address it. # 7th July 2021, 10:29 pm

Query Engines: Push vs. Pull (via) Justin Jaffray (who has worked on Materialize) explains the difference between push and pull query execution engines using some really clear examples built around JavaScript generators. # 2nd May 2021, 2:49 am

A Complete Guide To Accessible Front-End Components. I’m so excited about this article: it brings together an absolute wealth of resources on accessible front-end components, including many existing component implementations that are accessible out of the box. Date pickers, autocomplete widgets, modals, menus—all sorts of things that I’ve been dragging my heels on implementing because I didn’t fully understand their accessibility implications. # 23rd March 2021, 1:06 am

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

hooks-in-a-nutshell.js (via) Neat, heavily annotated implementation of React-style hooks in pure JavaScript, really useful for understanding how they work. # 4th January 2021, 6:36 pm