Simon Willison’s Weblog

Blogmarks tagged javascript

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Refactoring optional chaining into a large codebase: lessons learned (via) JavaScript now supports foo?.bar?.baz?.() optional chaining syntax across all major browsers. Lea Verou provides the definitive guide to using it to refactor code. # 18th June 2020, 3:23 pm

Deno 1.0. Deno is a new take on server-side JavaScript from a team lead by Ryan Dahl, who originally created Node.js. It’s built using Rust and crammed with fascinating ideas—like the ability to import code directly from a URL. # 13th May 2020, 11:38 pm

New developer features in Firefox 75 (via) Firefox 75 just came out with a bunch of new developer features. My favourite is instant evaluation in the JavaScript console: any statement without side effects now shows a preview of its results as you type. # 7th April 2020, 7:23 pm

gifcap (via) This is really neat: a purely client-side implementation of animated gif screen capture, using navigator.mediaDevices.getDisplayMedia for the screen capturing, mithril for the UI and the gif.js pure JavaScript GIF encoding library to render the output. # 30th March 2020, 9:29 pm

2020 Web Milestones (via) A lot of stuff is happening in 2020! Mike Sherov rounds it up—highlights include the release of Chromium Edge (Microsoft’s Chrome-powered browser for Windows 7+), Web Components supported in every major browser, Deno 1.x, SameSite Cookies turned on by default (which should dramatically reduce CSRF exposure) and Python 2 and Flash EOLs. # 24th January 2020, 4:43 am

Snowpack (via) Really interesting new twist on build systems for JavaScript. Modern browsers (everything since IE11) support JavaScript modules, but actually working with them is tricky since so much of the JavaScript ecosystem expects you to be using a bundler like Webpack. Snowpack is a tool for converting npm dependencies into JavaScript modules which can then be loaded directly by the browser, taking advantage of HTTP/2 to efficiently load the resulting larger number of files. # 10th January 2020, 5:06 am

μPlot (via) “An exceptionally fast, tiny time series chart. [...] from a cold start it can create an interactive chart containing 150,000 data points in 40ms. [...] at < 10 KB, it’s likely the smallest and fastest time series plotter that doesn’t make use of WebGL shaders or WASM” # 14th October 2019, 11:03 pm

Optimizing for the mobile web: Moving from Angular to Preact. Grubhub reduced their mobile web load times from 9-11s to 3-4s by replacing Angular with Preact (and replacing other libraries such as lodash with native JavaScript code). The conversion took 6 months and involved running Angular and Preact simultaneously during the transition—not a huge additional overhead as Preact itself is only 4KB. They used TypeScript throughout and credit it with providing a great deal of confidence and productivity to the overall refactoring. # 5th August 2019, 12:26 pm

When should you be using Web Workers? 85% of worldwide mobile devices are massively less performant than high end iPhones. Surma argues that we should be making aggressive use of Web Workers to keep as much of our JavaScript as possible off the main UI thread, to avoid freezing up the entire interface. # 15th June 2019, 4:31 am

Monaco Editor. VS Code is MIT licensed and built on top of Electron. I thought “huh, I wonder if I could run the editor component embedded in a web app”—and it turns out Microsoft have already extracted out the code editor component into an open source JavaScript package called Monaco. Looks very slick, though sadly it’s not supported in mobile browsers. # 21st May 2019, 8:47 pm

How Does React Tell a Class from a Function? (via) Understanding the answer requires a deep understanding of the history of the JavaScript class system plus how Babel and other tools work with it. “For an API to be simple to use, you often need to consider the language semantics (possibly, for several languages, including future directions), runtime performance, ergonomics with and without compile-time steps, the state of the ecosystem and packaging solutions, early warnings, and many other things. The end result might not always be the most elegant, but it must be practical.” # 3rd December 2018, 1:30 am

BigInt: arbitrary-precision integers in JavaScript (via) The BigInt specification is now supported in Chrome—but it hasn’t yet made it to other browsers. The Chrome team have a really interesting solution: they’ve released a JSBI library which you can use to do BigInt calculations in any browser today, and an accompanying Babel plugin which can rewrite calls to that library into BigInt syntax once browser support catches up. I’ve never seen a library that includes a tool for refactoring itself into oblivion before. # 28th November 2018, 2:22 am

A Netflix Web Performance Case Study (via) Fascinating description of how Netflix knocked the 3G loading times of their homepage in half for logged-out users by rendering the React templates on the server-side and using the bare amount of vanilla JavaScript necessary to get the homepage interactive—then XHR prefetching the full React code needed to power the subsequent signup flow. Via Alex Russell, who tweets “I’m increasingly optimistic that we can cap JS emissions by quarantining legacy frameworks to the server side.” # 6th November 2018, 8:54 pm

Svelte RFC 0001: Reactive assignments (via) Svelte is a really interesting JavaScript framework: it offers a similar component-based developer experience to React but does it while delivering a tiny amount of code-to-the-browser thanks to being built entirely around a compiler that generates the minimum code necessary. In this RFC the Svelte team propose taking this approach even further, by generating code to accompany every relevant variable assignment that can trigger the corresponding view update. The document also has a very clear explanation of how React, Vue and current Svelte differ in their solutions to the challenge of updating the visible HTML view when the corresponding state changes. # 3rd November 2018, 4:58 pm

matthewp/haunted: React’s Hooks API implemented for web components (via) It’s been fascinating over the past few days watching various frontend web stacks start playing with the new ideas introduced by the proposed React hooks API. lit-html is one of my favourite React alternatives—it’s built on web components and makes really clever use of ES6 template literals (in place of React’s JSX, which requires an additional compilation step). With Haunted Matthew Phillips explores the combination of lit-html, web components and hooks-style state management. # 31st October 2018, 1:04 am

Sqorn (via) JavaScript library for building SQL queries that makes really smart usage of ES6 tagged template literals. The magic of tagged template literals is that they let you intercept and process interpolated values, making them ideally suited to escaping parameters in SQL queries. Sqorn takes that basic ability and layers on some really interesting API design to allow you to further compose queries. # 19th September 2018, 6:34 pm

Tech Notes: TypeScript at Google (via) In which Evan Martin provides some fascinating colour on the state of JavaScript tooling within Google, which has some unique challenges given that Gmail is 14 years old now and Google have evolved their own internal JavaScript stack which differs widely from the rest of the industry (mainly because it predates most of the successful open source tools). “Which leads me to the middle path, which my little team has been pursuing: incrementally adopt some external tooling where it makes sense, by figuring out how to make it interoperate with our existing code base.” # 2nd September 2018, 7:08 pm

A tour of JavaScript timers on the web (via) Do you understand the differences between setTimeout, setInterval, setImmediate, requestAnimationFrame and requestIdleCallback? I didn’t. # 2nd September 2018, 10:10 am

6 Great Uses of the Spread Operator. As I’ve been getting more comfortable with 2018-era JavaScript the spread operator and object restructuring are two of the features I have found most interesting. # 22nd August 2018, 3:17 pm

Observable Tutorial 2: Dog pictures (via) Observable have a neat new set of tutorials on how to get started with their reactive notebooks. You don’t even need to sign up for the service: they have a “Scratchpad” link in their navigation bar now which lets you spin up a test notebook with one click. # 18th August 2018, 7:55 pm

ES6 In Depth: Template strings. Useful guide to the advanced features of backtick template strings in ES6. # 17th July 2018, 4:08 pm

Feature comparison between hyperHTML and lit-html. Compiled by hyperHTML author Andrea Giammarchi. lit-html is a similar project maintained by Google’s Polymer team. # 17th July 2018, 3:58 pm

hyperHTML (via) I’ve been playing around with multiline backtick template literals in JavaScript recently, and Claudio Cicali on Twitter pointed me to hyperHTML. It’s a fascinating project: it implements an alternative to React’s virtual DOM in just 4.6KB of code, taking advantage of the way tagged template literals can call a custom function which gets to affect how the interpolated values from the template are treated. The documentation does a great job of describing the various clever tricks that are used under the hood, in particular the way it takes advantage of the way tagged literals “freeze” the incoming array of literal chunks allowing hyperHTML to compile each template once and reuse the complied version for different interpolations. # 17th July 2018, 3:39 pm

future-fstrings (via) Clever module that backports fstrings to versions of Python earlier than 3.6, by registering itself as a codec and abusing Python’s # -*- coding: future_fstrings -*- feature. Via a conversation on Twitter that pointed out that the JavaScript community have been using transpilation to successfully experiment with new language features for years now. # 13th July 2018, 4:39 am

react-from-zero (via) Interesting approach to teaching and understanding React: unlike most other tutorials this skips Webpack and ES6 entirely an focuses on things you can get running just using a browser and loading code via script tags. It does eventually load Babel to enable client-side JSX transforms, but before that it shows how React can be used by loading react.js and react-dom.js and then calling React.createElement() manually (or by using the 0xeac7 magic symbol and constructing JavaScript objects manually with $$typeof: magicValue). # 3rd July 2018, 5:27 pm

source-map-explorer. Very neat tool for creating a tree map visualization of the size of the components of a bundled JavaScript file created by webpack (or if you’re using create-react-app by “npm run build”). I ran this using “npx source-map-explorer build/static/js/main.d63f3f34.js” (since I don’t like using “npm install -g”). # 24th June 2018, 9:37 pm

Notebook: How to build a Teachable Machine with TensorFlow.js (via) This is a really cool Observable notebook. It explains how to build image classification that runs in the browser on top of Tensorflow.js, and includes interactive demos that hook into your webcam and let you hold up items and use them to train a classifier. Since it’s built on Observable every single underlying line of source code is available to browse as part of the essay. # 20th June 2018, 9:10 pm

Changelog 2018-06-12 / Observable. The ability to download an Observable notebook as a stand-alone ES module and run it anywhere using their open source runtime is fascinating, but it’s also worth reading the changelog for some of the new clever tricks they are pulling using await—“await visibility();” in a notebook cell will cause execution to pause until the cell scrolls into view for example. # 13th June 2018, 3:50 pm

Observable: Downloading and Embedding Notebooks (via) Big news from the Observable team: firstly, they’ve released the open source runtime for their notebooks which means you can now execute the code from a notebook independently of their hosted service. On top of that they’ve constructed an elegant way of exporting and executing notebooks (or specific notebook cells) as ES6 modules and as installable npm package tarballs. # 22nd May 2018, 12:14 pm

sql.js Online SQL interpreter (via) This is fascinating: sql.js is a project that complies the whole of SQLite to JavaScript using Emscripten. The demo is an online SQL interpreter which lets you import an existing SQLite database from your filesystem and run queries against it directly in your browser. # 17th May 2018, 9:28 pm

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