Patrick Dubroy
@dubroy.com
1.5K followers
260 following
520 posts
Programmer & researcher, co-creator of https://ohmjs.org. 🇨🇦 🇩🇪 🇪🇺
Co-author of https://wasmgroundup.com — learn Wasm by building a simple compiler in JavaScript.
Prev: CDG/HARC, Google, BumpTop
Posts
Media
Videos
Starter Packs
Pinned
![After learning about FinalizationRegistry, I also learned about the using statement:
The using declaration declares block-scoped local variables that are synchronously disposed. Like const, variables declared with using must be initialized and cannot be reassigned. The variable's value must be either null, undefined, or an object with a [Symbol.dispose]() method. When the variable goes out of scope, the [Symbol.dispose]() method of the object is called, to ensure that resources are freed.
It's useful in scenarios where you might otherwise use a try/finally, e.g.:
let normalMap;
try {
tex = textureLoader.load('muppet.jpg');
tex.doSomething();
// …
} finally {
tex.dispose();
}
With a using statement, and assuming the texture object implemented [Symbol.dispose](), you could write it like this instead:
using tex = textureLoader.load('muppet.jpg');
tex.doSomething();
[Symbol.dispose]() will be called when tex goes out of scope. Unlike FinalizationRegistry — but just like a finally block — it's guaranteed to be called, so you can depend on it (in environments that support it).
It's currently supported in Chromium-based browsers, Node, and Firefox, but not yet in Safari. It's also been supported in TypeScript since v5.2, which was released in August 2023.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:zcycfvljdjkc2ywtj33blgdl/bafkreidukmuj4ospd7bsbl7rbpe6e5rydnbw2qqgkofxtwznwr5q35aaya@jpeg)
![Required dispose
A non-obvious thing is how to deal with objects that must be disposed. In other words, if a programmer accidentally writes const instead of using, can we catch it? For many scenarios, we can — by writing a getter for [Symbol.dispose]():
import assert from 'node:assert/strict';
class MyResource {
constructor() {
this._using = false;
}
doSomething() {
assert(this._using, 'Did you forget `using`?');
// …
}
get [Symbol.dispose]() {
this._using = true;
return () => {
// Actual dispose logic goes here.
}
}
}
using res1 = new MyResource(); // ok
const res2 = new MyResource();
res2.doSomething(); // Throws](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:zcycfvljdjkc2ywtj33blgdl/bafkreicqcjuhplvwl5lhbsz2bm2oukphpanscstaquhqdmjvmvt2kqvyki@jpeg)
![sources
Type: string | string[]
Files or directories that this task uses as input, if this and outputs is defined, mise will skip executing tasks where the modification time of the oldest output file is newer than the modification time of the newest source file. This is useful for tasks that are expensive to run and only need to be run when their inputs change.
The task itself will be automatically added as a source, so if you edit the definition that will also cause the task to be run.
This is also used in mise watch to know which files/directories to watch.
This can be specified with relative paths to the config file and/or with glob patterns, e.g.: src/**/*.rs. Ensure you don't go crazy with adding a ton of files in a glob though—mise has to scan each and every one to check the timestamp.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:zcycfvljdjkc2ywtj33blgdl/bafkreiez4ci5nw4xbkutuv2cjdplo3latbwrughvn2hb2kv5oki424dkhm@jpeg)
Reposted by Patrick Dubroy
Patrick Dubroy
@dubroy.com
· 10d
Patrick Dubroy
@dubroy.com
· 10d
![A heading reading "JSON with labels and numbers", followed by the following monspace-formatted text:
[
["Bananas", 5],
["Apples", 4],
["Oranges", 3]
]](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:zcycfvljdjkc2ywtj33blgdl/bafkreiebqbb6eikjily2mqg55yaauxkwl3dkakl3fmovge6lap7w5h4eou@jpeg)
