proposal-shadowrealm
quickjs-emscripten
proposal-shadowrealm | quickjs-emscripten | |
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19 | 21 | |
1,376 | 1,130 | |
1.2% | - | |
6.0 | 9.4 | |
13 days ago | 18 days ago | |
HTML | TypeScript | |
- | GNU General Public License v3.0 or later |
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For example, an activity of 9.0 indicates that a project is amongst the top 10% of the most actively developed projects that we are tracking.
proposal-shadowrealm
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Updates from the 98th TC39 meeting
ShadowRealm: ECMAScript Proposal, specs, and reference implementation for Realms [Stage 3 -> 2].
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Should you use jest as a testing library?
You can't out of the box. There is an open issue on the Node.js repositoryto let the node:vm module to use the vm's context, but it is still open. It seems that the Node.js core team is interested in fixing this problem by implementing the new ShadowRealm spec, and I think we will make some progress during 2023.
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Building an Extension System on the Web
ShadowRealms — a successor of the Realms proposals, this API is intended for use cases exactly like plugins or extension systems, providing an option for creating distinct global environments to run the code in. While not entirely secure on its own, this API could provide a strong foundation to build actual extension systems on the Web. That said, 4 years later, the TC39 proposal is currently only at stage 3, not implemented by any browser;
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Vitest vs Jest benchmarks on a 5 year old real work SPA
With --no-isolate it was 2.8x faster than vitest and 1.7x faster than Jest, but 19 tests failed (see table above). Some people report issues with watch mode when using --no-isolate. So I decided to not pursue it any further. Once the vm module that Vitest relies on supports ESM, or when the amazingly named Shadow Realms are added to JavaScript, we will likely get this performance boost for free without the downsides.
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Improving Vitest Performance
If ShadowRealms are ever added to EcmaScript (and implemented into V8/Node) they'll allow for a different approach to isolating code that would be faster without the downsides of sharing global.
- Virtualization is not an important enough use case for the web platform to tradeoff ergonomics and possible confusion for web devs, who by and large […] do not understand the separation between the specs. More to the point, they really shouldn't need to.
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Is there an npm package for perchance?
Eventually I will get around to creating a "proper" package by just grabbing all the JS that is loaded by the code in the iframe, and bundling it up. We really need the ShadowRealm proposal to go through because the perchance engine messes with a lot of JS internals, so it would mess up the rest of your app. Could do it in a WebWorker, but then everything would have to be async.
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Show HN: Run unsafe user generated JavaScript in the browser
The upcoming JavaScript Shadow Realms proposal looks like it solves a similar problem: https://github.com/tc39/proposal-shadowrealm/blob/main/expla...
- Named Element IDs Can Be Referenced as JavaScript Globals
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Running user code in the browser (for a leetcode clone)
Browser-based JavaScript doesn't yet have a way to isolate code fully in this manner though there is a new JavaScript feature on the way that would provide this capability. Its called ShadowRealm and would basically give you a new global context to execute code that's completely separate from your main document code.
quickjs-emscripten
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New QuickJS Release
Based on your comment below I think you figured out the difference - but if you're looking to execute JS, you can pick between ShadowRealm (where available, or using a polyfill) or my library quickjs-emscripten.
Pros of quickjs-emscripten over ShadowRealm:
- You can use quickjs today in any browser with WASM. ShadowRealm isn't available yet, and polyfills have had security issues in the past. See https://www.figma.com/blog/an-update-on-plugin-security/
- In ShadowRealm eval, untrusted code can consume arbitrary CPU cycles. With QuickJS, you can control the CPU time used during an `eval` using an [interrupt handler] that's called periodically during the eval.
- In ShadowRealm eval, untrusted code can allocate arbitrary amounts of memory. With QuickJS, you can control both the [stack size] and the [heap size] available inside the runtime.
- quickjs-emscripten can do interesting things with custom module loaders and facades that allow synchronous code inside the runtime to call async code on the host.
Pros of ShadowRealm over QuickJS:
- ShadowRealm will (presumably?) execute code using your native runtime, probably v8, JavaScriptCore, or SpiderMonkey. Quickjs is orders of magnitude slower than JIT'd javascript performance of v8 etc. It's also slower than v8/JSC's interpreters, although not by a huge amount. See [benchmarks] from 2019.
- You can easily call and pass values to ShadowRealm imported functions. Talking to quickjs-emscripten guest code requires a lot of fiddly and manual object building.
- Overall the quickjs(-emscripten) API is verbose, and requires manual memory management of references to values inside the quickjs runtime.
[interrupt handler]: https://github.com/justjake/quickjs-emscripten/blob/main/doc...
[stack size]: https://github.com/justjake/quickjs-emscripten/blob/main/doc...
[heap size]: https://github.com/justjake/quickjs-emscripten/blob/main/doc...
[benchmarks]: https://bellard.org/quickjs/bench.html
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Extism Makes WebAssembly Easy
The thing I want to achieve with WebAssembly is still proving a lot harder than I had anticipated.
I want to be able to take strings of untrusted code provided by users and execute them in a safe sandbox.
I have all sorts of things I want this for - think custom templates for a web application, custom workflow automation scripts (Zapier-style), running transformations against JSON data.
When you're dealing with untrusted code you need a really robust sandbox. WebAssembly really should be that sandbox.
I'd like to support Python, JavaScript and maybe other languages too. I want to take a user-provided string of code in one of those languages and execute that in a sandbox with a strict limit on both memory usage and time taken (so I can't be crashed by a "while True" loop). If memory or time limit are exceeded, I want to get an exception which I can catch and return an error message to the user.
I've been exploring options for this for quite a while now. The furthest I've got was running Pyodide inside of Deno: https://til.simonwillison.net/deno/pyodide-sandbox
Surprisingly I've not found a good pattern for running a JavaScript interpreter in a WASM sandbox yet. https://github.com/justjake/quickjs-emscripten looks promising but I've not found the right recipe to call it from server-side Python or Deno yet.
Can Extism help with this? I'm confident I'm not the only person who's looking for a solution here!
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Node on Web. Use Nodejs freely in your browser with Linux infrastructure.
"Safely execute untrusted Javascript in your Javascript, and execute synchronous code that uses async functions" quickjs-emscripten, NPM
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Sandboxing JavaScript Code
This maybe, as a start?
https://github.com/justjake/quickjs-emscripten
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Hacker News top posts: Nov 20, 2022
QuickJS Running in WebAssembly\ (17 comments)
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QuickJS Running in WebAssembly
The library was inspired by Figma’s blog posts about their plug-in system: https://github.com/justjake/quickjs-emscripten#background
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Show HN: Run unsafe user generated JavaScript in the browser
If you need to call into user-generated Javascript synchronously or have greater control over the sandbox environment, you can use WebAssembly to run a Javascript interpreter: https://github.com/justjake/quickjs-emscripten#quickjs-emscr...
QuickJS in WebAssembly is much slower than your browser's native Javascript runtime, but possibly faster than async calls using postMessage. As an added bonus, it can make async functions in the host appear to be synchronous inside the sandbox using asyncify: https://emscripten.org/docs/porting/asyncify.html.
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Why Would Anyone Need JavaScript Generator Functions?
You can use One Weird Trick with generator functions to make your code "generic" over synchronicity. I use this technique to avoid needing to implement both sync and async versions of some functions in my quickjs-emscripten library.
The great part about this technique as a library author is that unlike choosing to use a Promise return type, this technique is invisible in my public API. I can write a function like `export function coolAlgorithm(getData: (request: I) => O | Promise): R | Promise`, and we get automatic performance improvement if the user's function happens to return synchronously, without mystery generator stuff showing up in the function signature.
Helper to make a function that can be either sync or async: https://github.com/justjake/quickjs-emscripten/blob/ff211447...
Uses: https://cs.github.com/justjake/quickjs-emscripten?q=yield*+l...
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Why Am I Excited About WebAssembly?
This seems like a pretty nice, recently enabled way of getting a sandboxed js environment: QuickJS compiled to WASM: https://github.com/justjake/quickjs-emscripten.
What are some alternatives?
wtfjs - 🤪 A list of funny and tricky JavaScript examples
wasmtime - A fast and secure runtime for WebAssembly
Pentive - Collaborative Spaced Repetition
wasmer - 🚀 The leading Wasm Runtime supporting WASIX, WASI and Emscripten
vm2-process - Execute unsafe javascript code in a sandbox
wizer - The WebAssembly Pre-Initializer
vrite - Open-source developer content platform
rr - Record and Replay Framework
caja - Caja is a tool for safely embedding third party HTML, CSS and JavaScript in your website.
go - The Go programming language
LavaMoat - tools for sandboxing your dependency graph
iPlug2 - C++ Audio Plug-in Framework for desktop, mobile and web