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Show HN: Nsynjs – JS engine with stoppable threads and without callback hell (github.com)
51 points by kidstrack on May 24, 2017 | hide | past | web | favorite | 57 comments

So it stringifies the function you give it, splits it into its component bits of execution, then interprets the contents alongside a state machine (with judicious use of bits concatenated together and eval'd). Interesting, for sure. AFAIK there's no preemption mechanism (or resource management), so all it does is make your code execute asynchronously - very asynchronously - the every-line-interwoven-randomly kind of asynchronously.

I do love me some metaprogramming, but is there a real scenario where you'd want something as dangerous as this compared to a generator (or a system of generators)? They have very clear atomicity guarantees (things between yields will happen synchronously), unlike what this ends up decomposing your code into. I suppose that's just the cooperative vs supervised threading debate, though?

So interesting project! I'm skeptical on the practicality of it but it's still interesting.

>> global.nsynjs = global.nsynjs || require('nsynjs');

Don't do this. The module pattern is pretty well known and you can use it to return a singleton. Global has some built in node.js stuff but I wouldn't mess with it.

>> Example of wrapper to setTimeout, that will be gracefully stopped in case if pseudo-thread is stopped:

This seems overly complex and unintuitive. Also, there are lots of references to `synjs` but the project's name is `nsynjs` which seemed confusing to me.

Honestly, like I mentioned at first, cool project but callback hell is very easy to avoid even without Promises or async / await as long as you follow solid development patterns.

I would be interested if you have benchmarks / comparisons against callbacks, promises and async / await.

Thanks for the feedback.

"wrapper to setTimeout...This seems overly complex and unintuitive"

Typical web app most likely would have very few wrappers ($.ajax, setTimeout, etc), and they need to be written only once. But then everywhere in nsynjs-executed code you can just use them, connect with any necessary logic that JS can offer (not only by chaining .then...then.), without thinking what function is async/await and when it actually executed. My intention was to be able to write logic on JS in step-by-step manner the same way as if it was Visual Basic.

> The module pattern is pretty well known and you can use it to return a singleton.

How would you even make it _not_ return a singleton? I thought that was default.

One way is to delete entries from `require.cache`.

Either way you might get a separate instance if npm decided that your module and another module require different version of a given module. These would both be singletons though. Just singletons of instances of different versions of the same module.

It is, I only meant that's a way it can be handled not that it wasn't common or anything.

Reminds me of `node-fibers`[1]

    var Fiber = require('fibers');

    function sleep(ms) {
        var fiber = Fiber.current;
        setTimeout(function() {
        }, ms);

    Fiber(function() {
        console.log('wait... ' + new Date);
        console.log('ok... ' + new Date);
    console.log('back in main');
It is used heavily in meteor[2]

1: https://github.com/laverdet/node-fibers 2: https://github.com/meteor/meteor

Could you please not advocate SQLinjection in your example code?

> friends: dbQuery("select * from firends where user_id = "+userId).data,

> comments: dbQuery("select * from comments where user_id = "+userId).data,

> likes: dbQuery("select * from likes where user_id = "+userId).data

I'm no js developer, but there has to be a way of using prepared statements, even if just for sample code.

It's not 2001 anymore, security is important!

I agree with you. It's just for illustration purposes I intentionally oversimplified it to pseudo-code.

That's the wrong thing to be oversimplifying, tbh.

I don't see the problem if userId is guaranteed to be just an id.

This can be done, for example, by testing it before the SQL call. In that case, it's safer than most pointer-dereferences done in C++.

That's one hell of an `if` you've got there.

Not that big of an if. The id was most likely pulled out of the database itself in cases like:

>friends: dbQuery("select * from firends where user_id = "+userId).data

or it was pulled from a GET parameter.

The point is that regardless of where it came from parameterized queries are a staple of programming now, and having an example without it would be like having an example of a login system be

    if (username in db && password in db) { login() }

I'd much rather read a straightforward example like that in an intro, then reading the complicated prepared statement when going through what's essentially pseudocode.

There are valid cases where you're sure that the thing you're looking at is a valid id (ie. you already pulled it out of the database or by generating it yourself), not every program is a webapp that's handling user input, and examples like this aren't meant to teach you best security practices.

And yes the login system example would be acceptable if you're discussing something entirely unrelated to actually implementing one.

I think the disconnect here is that a prepared statement isn't really more complicated. As pseudocode it's more like

    dbquery('select * from friends where user_id = $1', userId)
A few extra characters is all it takes.

And the benefits of prepared or parameterized statements don't end at security, they can often have performance benefits as well.

And as for the login pseudocode, if it doesn't have anything to do with the example, hide the implementation:

    if (userIsAuthenticated === true) { login() }

I've been enjoying sql-template-strings lately, which build on ES6 tagged template literals so you get the best of both worlds:

    dbquery(sql`select * from friends where user_id = ${userId}`)

(not sure why you are getting downvoted, but...)

Template strings are the one ES2015 feature I still really haven't used much. And this almost seems like a textbook use case for them! I'll need to give this a shot in a toy project and see if I can't get my own version hacked together for support with my favorite database interface library in node (pg-promise)

What's wrong with async/await?

Even as a huge async/await fan, this is a great explanation of the problem: http://journal.stuffwithstuff.com/2015/02/01/what-color-is-y...

VMs that offer lightweight, blocking, non-shared memory, threads provide a great developer experience. The Dart team was experimenting with this with the Fletch VM.

While it gives good insight to the problem of sync vs async functions, I've come to find its conclusions problematic (and it rather blatantly ignores Chesterton's fence), especially with "Java did it right, but they have started to do it badly now", and especially "Go has eliminated the distinction between synchronous and asynchronous code". Ouch. You are going to think that - until your hit first deadlock or race condition.

While implementation quality of the "colored function" concept varies greatly (and JS async/await is not a good example IMO - look at C# for one that doesn't neccesarily suffer the "async all the way up" problem, for example), there are reasons it's so prevalent. Async is fundamentally different, and more importantly: In the end, it's all about the data.

That's why the most important part of goroutines is the channel/send/receive(EDIT: And especially select, of course. :)) implementation. And that's why the simple "go func" syntax itself or whether it's different from normal function is a bit of a red herring, since the implementation and data access/communication inside the function will likely be different.

I don't know why you're getting downvoted, you're right.

I love Go, it's my language of choice. There's a clear difference between calling a function sync or async. It's nice that we can choose to do either at will.

Oh, except that if it's an async call we have to use channels to communicate with it. Which is cool, but it's a different mechanism than if it's a sync call.

It's exactly the same as the red/blue rant about JS. If it's async you have to hand it a channel to talk to you on. If it's sync you can just wait for it to return. Async/Await same same but different.

Yes, the language does some nice stuff under the covers about pausing goroutines, but it only does that if you have multiple goroutines. If you code everything without using goroutines (and channels) then it's not concurrent and won't do the nice stuff. It'll pause for i/o just like any other language.

When calling a function, you know what arguments/parameters to use, right!? Then you also know if it's sync or async. The browsers way of dealing with async seems to be forgotten, for example:

  button.onclick = buttonClicked;
I find this pattern easier to deal with then callbacks.

While I don't use async / await right now, mostly because it's not natively available in all of the target browsers I want to use, I'm not the biggest fan of the pattern. It takes previously asynchronous functions and makes them appear as synchronous. The worst part is with some asynchronous methods you can't use async / await so now you have synchronous and asynchronous code that appears identical while also having some other asynchronous code that appears more traditional.

Overall it just ends up being a bit inconsistent for my tastes. But I like that we're trying more things to evolve the language to avoid common pitfalls like callback hell

It's funny watching part of the history of C# replay itself in Js, I heard the same arguments when it was playing out in C# (TPL => Promises, await/async => await/async)

It's a kludge. Syntactic sugar to remove one level of nesting.

Other languages come either with great concurrency support out of the box (Go, Erlang) or enough constructs to implement cooperative schedulers without having to specify async/await (Lua).

Not disagreeing, but as a long time JavaScripter it is remarkable to me that no matter how delightful or expressive or ergonomic the language tries to become, the same old criticisms manage to evolve with it (this may not be unique to JS).

[Edit] JS has long been criticized (fairly or not) for offering clunky "concurrency" strategies. If you must down vote, please have the decency to offer a counter perspective.

As someone who has been around for a long time and manages teams using many different languages (C,C++,C#,Java,Python,JavaScript) my JavaScript/Web teams are the most problematic in terms of cost/performance/gating bugs/upgrades/multi-platform support. The JavaScript critiques that you see are just an expression of the time and resources being wasted.

Where in the stack did you spend your time before you became a manager?

If you have callbacks, you end up with hard to read and debug code.

If you have transparent async, then:

Then how do you know what blocks and what doesn't ? What's asynchronous and what's going to trigger a switch ? What's a disguised callback and what's the next line ?

What's the solution then ?

Why would you need to know, except in some special cases? If you're using async/await, your next line is not executing anyway until the result comes, blocking or not.

Because otherwise you block the even loop or mismatch life cycle. Espacially reading an unfamiliar code base.

embrace higher-order functions. Use named functions and closures!

example code:

  var anchors = document.getElementsByTagName(“a”);
  for(var i=0,len=anchors.length; i<len; i++){
    alertClickAnchor(i); // Named function

  function alertClickAnchor(i) { // Closure
    anchors[i].onclick = function() {

This makes anything but basic life cycles very hard to read.

You can look at each function at a time and only have to understand what that function does. No more nesting.

What's wrong with that?

2 main reasons: 1. If some nested function is async/await, all the callers (and whole graph) need to be converted to async/await. I feel that language shouldn't force programmer to do this type of tedious work. 2. It's not compatible with some browsers, only via Babel

In JS async/await returns a promise. In Python you have asyncio.ensure_future() to schedule coroutines. You can always call async code from sync code.

> If some nested function is async/await, all the callers (and whole graph) need to be converted to async/await

Is totally false. You can await on any promise, the method called doesn't have to be an async function.

And you can resolve any async function through promises as well.

> 2. It's not compatible with some browsers, only via Babel

async/await is part of the the ES spec, which browsers have to follow to be compliant with ES spec.

#1 is a misleading claim. An async function returns a promise when called, which can be used in any non-async context.

I think the claim was: One async function (which of course returns a Promise under the hood) forces all surrounding functions to be also asynchronous (return a promise). Of course you could start an async operation from any function -> Just call the async function and ignore the result. But in order to do something with the result and return a transformed version of it the surrounding function has to be async (return a Promise, accept callbacks, etc) too.

Maybe the confusion was the async here has two meanings:

1. asynchronous in general, which means it doesn't return a result immediately, but returns it through a Promise which is fulfilled later or a callback.

2. Using the async/await syntax. As we all agree this one is just sugar around Promises.

I'm using ES6 async/await and I can't be happier, async programming is almost sane now. The only drawback is that you have to remember that it's all syntax sugar about Promises and they are just a bit more than syntax sugar about callbacks, so you have to understand how each async thing works or you'll be mad. But when you know those things, you can be asynchronously productive.

Sightly related question, is there a library that

- takes in a function and returns a promise returning function

- the new function will use a web worker in the browser and something like a thread worker in NodeJs.

- isomorphic, as in same API in browser as in the server (so maybe usable in nextjs and nuxtjs based applications

Just curious if anything like that exists.

The JavaScript callback hell thing is pretty much solved now isn't it?

yes. I also never had it in the first place.

Having to manually handle callbacks (and error callbacks) is the hell in itself.

Fair enough :D

I can't quite see the need of this now we have async/await.

Me too. For the sake of sanity we should stick with async / await and forget the time we had to choose from dozens of different ways of doing async code (most of time requiring tedious wrappers).

Lets the winner takes it all.

async/await doesn't change the fact that we have two types of functions, async and sync.

How is this an improvement over `await` and `async`?


> Wrong wrong wrong wrong, wrong wrong wrong wrong! https://www.youtu...

What kind of person do you have to be to act like this when people try to show what they have made? Very sad.

Have some sense of humor. I would not take that literally / seriously.

I would rather focus on the next paragraph which is the one that matters.

Green threads are threads too (a.k.a. cooperative threads/coroutines).

It is my understanding they would always execute on the same core.

> It is my understanding they would always execute on the same core.

no they don't, Go has green threads and they are fully parallel. They are called green because they are not scheduled by the operating system.

I was referring to node.

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