Simon Willison’s Weblog

The first four Val Town runtimes (via) Val Town solves one of my favourite technical problems: how to run untrusted code in a safe sandbox. They’re on their fourth iteration of this now, currently using a Node.js application that launches Deno sub-processes using the deno-vm npm package and runs code in those, taking advantage of the Deno sandboxing mechanism and terminating processes that take too long in order to protect against while(true) style attacks. # 8th February 2024, 6:38 pm

A framework for building Open Graph images. GitHub’s new social preview images are generated by a Node.js script that fetches data from their GraphQL API, generates an HTML version of the card and then grabs a PNG snapshot of it using Puppeteer. It takes an average of 280ms to serve an image and generates around 2 million unique images a day. Interestingly, they found that bumping the available RAM from 512MB up to 513MB had a big effect on performance, because Chromium detects devices on 512MB or less and switches some processes from parallel to sequential. # 22nd June 2021, 9:25 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

elasticsearch-dump. Neat open source utility by TaskRabbit for importing and exporting data in bulk from Elasticsearch. It can copy data from one Elasticsearch cluster directly to another or to an intermediary file, making it a swiss-army knife for migrating data around. I successfully used the “docker run” incantation to execute it without needing to worry about having the correct version of Node.js installed. # 9th April 2018, 10:10 pm

github-trending-repos (via) This is a really clever hack: Vitaliy Potapov built a system for subscribing to a weekly digest of trending GitHub repos in your favourite languages entirely on top of the existing GitHub issues notification system. Find the issue for your particular language and hit “subscribe” and you’ll get an email (or push notification depending on how you get your issue notifications) once a week with the latest trends. The implementation is a 220 line Node.js script which runs on a daily and weekly schedule using Circle CI, so Vitaliy doesn’t even have to host or pay for any of the underlying infrastructure. It’s brilliant. # 23rd February 2018, 5:36 pm

Building a Full-Text Search App Using Docker and Elasticsearch. Deep, comprehensive tutorial from Patrick Triest showing how to use docker-compose to run three containers (Node API, nginx static content, elasticsearch) and then use that to build a neat Vue.js web search UI against 100 books from Project Gutenberg. # 1st February 2018, 3:41 pm

now-ab. Intriguing example of a Zeit Now microservice: now-ab is a Node.js HTTP proxy which proxies through to one of two or more other Now-deployed applications based on a cookie. If you don’t have the cookie, it picks a backend at random and sets the cookie. Admittedly this is the easiest part of implementing A/B testing (the hard part is the analytics: tracking exposures and conversions) but as an example of a microservice architectural pattern this is fascinating. # 16th November 2017, 11:03 pm

ZEIT – 6x Faster Now Uploads with HTTP/2 (via) Fantastic optimization write-up by Pranay Prakash. The Now deployment tool works by computing a hash for every local file in a project, then uploading just the ones that are missing. Pranay switched to uploading over HTTP/2 using the fetch-h2 library and got a 6x speedup for larger projects. # 8th November 2017, 1:04 am

Live htop. Neat, simplest-thing-that-could-possibly-work implementation of a tool that continually pipes the output of the htop command to a browser over a WebSocket. The htopgen.sh scripts loops every 2 seconds, runs htop, pipes it through a utility to convert the output to HTML and writes that to a file. Then the server.js Node.js script watches for changes to that file and pipes the entire file contents to the browser via socket.io. The index.html page in the browser subscribes to the WebSocket and updates the entire page using innerHTML every time it receives an event. # 1st November 2017, 6:07 pm

Carbon (via) Beautiful little tool that you can paste source code into to generate an image of that code with syntax highlighting applied, ready to be tweeted or shared anywhere that lets you share an image. Built in Node and next.js, with image generation handled client-side by the dom-to-image JavaScript library which loads HTML into a SVG foreignObject (sadly not yet supported by Safari) and uses that to populate a canvas and produce a PNG. # 19th October 2017, 6:31 pm

nodejitsu’s node-http-proxy (via) Exactly what I’ve been waiting for—a robust HTTP proxy library for Node that makes it trivial to proxy requests to a backend with custom proxy behaviour added in JavaScript. The example app adds an artificial delay to every request to simulate a slow connection, but other exciting potential use cases could include rate limiting, API key restriction, logging, load balancing, lint testing and more besides. # 28th July 2010, 11:34 pm

pdf.js. A JavaScript library for creating simple PDF files. Works (flakily) in your browser using a data:URI hack, but is also compatible with server-side JavaScript implementations such as Node.js. # 17th June 2010, 7:39 pm

Parsing file uploads at 500 mb/s with node.js. Handling file uploads is a real sweet spot for Node.js, especially now it has a high performance Buffer API for dealing with binary chunks of data. Felix Geisendörfer has released a new library called “formidable” which makes receiving file uploads (including HTML5 multiple uploads) easy, and uses some clever algorithmic tricks to dramatically speed up the processing of multipart data. # 2nd June 2010, 3:57 pm

A HTTP Proxy Server in 20 Lines of node.js. Proxying is definitely a sweet spot for Node.js. Peteris Krummins takes it a step further, adding host blacklists and an IP whitelist as configuration files and using Node’s watchFile method to automatically reload changes to them. # 28th April 2010, 1:24 pm

Step for Node.js. A further iteration on the attempts to make callback-based programming in Node.js easier to manage, this time making clever use of the ’this’ keyword to represent the next callback in the chain. # 13th April 2010, 11:02 am

webhook-relay. Another of my experiments with Node.js: webhook-relay is a self-contained queue and webhook request sending agent. Your application can POST to it specifying a webhook alert to be sent off, and webhook-relay will place that request in an in-memory queue and send it on its own time, avoiding the need for your main application server to block until the outgoing request has been processed. # 19th March 2010, 10:17 am

Node.js, redis, and resque (via) Paul Gross has been experimenting with Node.js proxies for allowing web applications to be upgraded without missing any requests. Here he places all incoming HTTP requests in a redis queue, then has his backend Rails servers consume requests from the queue and push the responses back on to a queue for Node to deliver. When the backend application is upgraded, requests remain in the queue and users see a few seconds of delay before their request is handled. It’s not production ready yet (POST requests aren’t handled, for example) but it’s a very interesting approach. # 28th February 2010, 11:02 pm

kriszyp’s node-promise. Another elegant approach to managing asynchronous flows in Node, including running things both in parallel and serial. # 28th February 2010, 3:50 pm

“Do” it fast! Tim Caswell’s Do library has been upgraded for compatibility with Node v0.1.30, and now has a clever Do.convert() method which wraps Node’s low-level APIs with the Do libraries “continuable” abstraction. # 22nd February 2010, 7:02 pm

node-v0.1.30 (via) A very significant new release of Node.js: the Twisted/Dojo-style Promise abstraction has been removed entirely, causing backwards incompatible changes to a bunch of core APIs. This means the pseudo-blocking Promise.wait() method is gone too, making it even harder to accidentally block your event loop. Instead, user-level libraries are encouraged to add Promise-style abstractions. I’m pleased to see Node sticking to the low-level stuff. # 22nd February 2010, 7 pm

do. A library for Node that adds a higher level abstraction for dealing with chained and parallel callbacks. # 17th February 2010, 5:43 pm

How To Node. New blog about Node.js, with a superb series of tutorials aimed at both experienced and new JavaScript developers. The stuff on managing callbacks (including running them in both series and parallel) is pretty eye-opening. # 17th February 2010, 5:42 pm

dogproxy. Another of my experiments with Node.js—this is a very simple HTTP proxy which addresses the dog pile effect (also known as the thundering herd) by watching out for multiple requests for a URL that is currently “in flight” and bundling them together. # 3rd February 2010, 1:05 pm

Hot Code Loading in Node.js. Blaine Cook’s patch for Node.js that enables Erlang-style hot code loading, so you can switch out your application logic without restarting the server or affecting existing requests. This could make deploying new versions of Node applications trivial. I’d love to see a Node hosting service that allows you to simply upload a script file and have it execute on the Web. # 31st January 2010, 1:57 pm