Do you, or the broader community, have any ideas about solving infinite loops? I'm on mobile so I can't test this at the moment, but I imagine that while(1) crashes the tab. What would an MVP operating system like ctrl-C functionality look like for execution environments in the browser?
Show HN: Scratch.js – Interactive JavaScript Scratchpad
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Re: Show HN: Scratch.js – Interactive JavaScript Scratchpad
#32Do you, or the broader community, have any ideas about solving infinite loops? I'm on mobile so I can't test this at the moment, but I imagine that while(1) crashes the tab. What would an MVP operating system like ctrl-C functionality look like for execution environments in the browser?
We started with a blacklist to match against while(1), while(true), for(;;), etc, but we eventually found an eslint plugin (goedel.js) that nicely tells you if the code contains an infinite loop or recursion.
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Re: Show HN: Scratch.js – Interactive JavaScript Scratchpad
#33Do you, or the broader community, have any ideas about solving infinite loops? I'm on mobile so I can't test this at the moment, but I imagine that while(1) crashes the tab. What would an MVP operating system like ctrl-C functionality look like for execution environments in the browser?
https://www.stopify.org/
To add to this comment, Stopify is a JS-to-JS compiler that instruments sync JS code to make them interruptible at set points. The paper [0] can explain it better than I ever could.
I work on an experimental Pyret [1] runtime that uses Stopify to instrument compiled Pyret code (plain old JS) so that we can run Pyret code on the main page thread without hanging it up. Main thread execution is important for quick/easy DOM access. In terms of performance cost, we haven't measured too extensively, but so far, on average, we're seeing a 2x slow down compared to un-Stopified programs.
(Disclaimer: paid contributor for Pyret).
Re: Show HN: Scratch.js – Interactive JavaScript Scratchpad
#34Do you, or the broader community, have any ideas about solving infinite loops? I'm on mobile so I can't test this at the moment, but I imagine that while(1) crashes the tab. What would an MVP operating system like ctrl-C functionality look like for execution environments in the browser?
https://www.stopify.org/
This is what I use. Seems to be the only option, and it works.
Re: Show HN: Scratch.js – Interactive JavaScript Scratchpad
#35Earlier quoted context omitted.
A timeout would most certainly not trigger during a busy loop in JS. Timeouts can only trigger when the main thread is not running code. Browsers will complain against code running for too long without interruption though.
Yes, as the other comments get at the "hack" I'm referring to is a loop transform that adds a timer check to the condition.
Oh, right, I was not there at all.
Wow, that seems hard to do. One would need to take a lot of things in account, including recursive calls, asynchronous functions / calls and, indeed, even long strings of instructions that are not necessarily part of a loop or recursive calls.
Would a transform that adds the check between every JS instructions where it is possible theoretically solve the problem? is there a solution that does not slow down the code too much and interrupts the code within an acceptable margin?
Re: Show HN: Scratch.js – Interactive JavaScript Scratchpad
#36Do you, or the broader community, have any ideas about solving infinite loops? I'm on mobile so I can't test this at the moment, but I imagine that while(1) crashes the tab. What would an MVP operating system like ctrl-C functionality look like for execution environments in the browser?
I have made something similar ( https://easylang.online/ide/ ). It is a language of its own, which is compiled and interpreted by WASM. The problem with hanging in endless loops is solved by running the interpreter in a "web worker" that can be killed and restarted at any time.
Looks interesting, I'll do some digging around. Thank you for sharing.
Re: Show HN: Scratch.js – Interactive JavaScript Scratchpad
#37The simplest scratchpad, which works in Firefox and Chromium at least.
data:text/html,Re: Show HN: Scratch.js – Interactive JavaScript Scratchpad
#38Do you, or the broader community, have any ideas about solving infinite loops? I'm on mobile so I can't test this at the moment, but I imagine that while(1) crashes the tab. What would an MVP operating system like ctrl-C functionality look like for execution environments in the browser?
Codepen uses a system that measures loop duration, and it's a giant pain. Having done some pens that do ray tracing and image transforms which can have long running loops. Given the variable execution time of JS it can be quite random. It just exits the loop without warning, causing weird failures in your code.
2 theoretical solutions ( with significant overhead ) are:
Run the code in a VM ( maybe quick.js compiled to WASM would work ) that suspends code execution periodically if it exceeds a certain duration. This has the advantage that long running code in general won't block rendering, not just loops.
Transform the AST to use async generator that yields once per loop. This would allow the loop to be suspended and resumed. But it would require a lot of modification to the AST, making effectively the entire call tree async.
Re: Show HN: Scratch.js – Interactive JavaScript Scratchpad
#39Can you give us Mac users some love and replace ctrl w/ command ? My muscle memory is giving me a hard time xD
The source is very small and can be used both through the file:// and hosted http protocols. So you can easily make it do whatever you like. I could maybe expose some global variables to make it customizable, but I went for simplicity and smaller source instead.
Ctrl-Enter is the shortcut for inserting a soft newline for content-editables on Safari btw. You might want to consider supporting command-enter for this reason alone.
Re: Show HN: Scratch.js – Interactive JavaScript Scratchpad
#40Do you, or the broader community, have any ideas about solving infinite loops? I'm on mobile so I can't test this at the moment, but I imagine that while(1) crashes the tab. What would an MVP operating system like ctrl-C functionality look like for execution environments in the browser?
We started with a blacklist to match against while(1), while(true), for(;;), etc, but we eventually found an eslint plugin (goedel.js) that nicely tells you if the code contains an infinite loop or recursion.
That plug-in certainly won’t cover all cases of infinite loops, or they just solved the halting problem :)