MuJS: an embeddable JavaScript interpreter

by Fenume • 11 years ago

100 56 11 years ago

Oh, is this from the ghostscript people?

kodablah2• 11 years ago

I understand the AGPL and the want to monetize the work, but it just feels so disingenuous to have to contact for commercial details.

chc3• 11 years ago

How is that disingenuous? It seems pretty forthright about its licensing to me.

kodablah2• 11 years ago

Because they have to be contacted to determine a price instead of making pricing clear. (I am not saying that they will not price consistently, I'm just saying it's a bit off-putting)

vgrichina• 11 years ago

So I guess this is slower than JavaScriptCore and you have to get commercial license to actually embed it. Why would one choose it at all?

chc3• 11 years ago

From the linked site:

"Why? Because V8, SpiderMonkey and JavaScriptCore are all too big and complex. MuJS's focus is on small size, correctness and simplicity."

xavel10• 11 years ago

About 'correctness' and 'small size' ... as soon as they'd add unittests as extensive as V8, JSCore, or SpiderMonkey, it'd grow big quite dramatically. :-)

I'd be interested to see how ES5-compliant MuJS really is. My guess is probably different from what they claim.

chj• 11 years ago

And JavaScriptCore actually has very solid API, if not simpler.

chubot2• 11 years ago

How does it compare with duktape: http://duktape.org/ ?

vortico• 11 years ago

I was wondering the same. It's nice having an alternative though. I consider there to be two C embeddable Javascript interpreters, Duktape and MuJS now. V8 and Spidermonkey are great, but they are not acceptable for small projects where a simple scripting language to extend functionality is needed.

robmccoll2• 11 years ago

One immediately apparent difference: duktape has a more liberal and commercial friendly license (MIT), while MuJS has a much more restrictive license (AGPL).

yellowapple3• 11 years ago

This is a pretty big deal for me. MuJS is a non-starter if I can't even use it in GPL'd software (let alone copyfree-licensed software; my preference for my own projects is the MIT license, so being able to include something without having to change that - as duktape offers - is ideal).

0x0• 11 years ago

Strange that the example has 'js_dofile("config.lua")'... Is there lua in here?

xavel10• 11 years ago

I noticed that too. My theory is that MuJS started out as a fork of Lua, with all sorts of Ecmascript-compat bolted on. Use with care, I suppose.

passthefist• 11 years ago

Which begs the question: why not use Lua to begin with, at least when starting a project? I totally get the use for this if you've got some existing JS and for some reason you need to talk to C. I've seen crazier things.

But I'd say the solution to 'I need a scripting language to talk to C' is solved very well by Lua.

*Edit:

After looking at the example it's C API is surprisingly similar to Lua's, even using such keywords as userdata. So that's interesting, considering they're really similar languages.

The function js_dofile doesn't look like it's doing anything with lua, nor can I find any use of lua at a cursory look at the source. I'd guess that since Lua and JS share syntax they are loading a .lua file with valid JS syntax.

yellowapple3• 11 years ago

I'm personally not a fan of Lua at all (nor am I a fan of Javascript...).

That said, there are plenty of other options out there. Even for JS embedding, there are projects like duktape that already address this need (supposedly; I haven't personally used duktape in any of my projects).

namuol• 11 years ago

Seeing as this was built by the creators of MuPDF [1], I'm guessing they built this because they need to use JS to support embedded JS forms.

1: http://www.mupdf.com/ (artifex)

nothrabannosir2• 11 years ago

I see hate for the licensing model they chose. But think of it this way: who is their target audience? Who would want a small, embeddable JS engine? I think they're targeting businesses who want to deploy node.js code on micro to small devices. Routers, NASes, that sort of thing.

xavel10• 11 years ago

And what if those companies wish to provide their software to customers? Enter a terrible hell of "how are we going to relicense our stuff", that'll most likely end up with said companies switching to a different library.

No, the GPL, especially the AGPL is inherently bad for libraries. Libraries, mind you, not software in general. Like I've written in my other comment, the LGPL solves this issue painlessly.

Besides that, node.js won't run with MuJS, because node.js depends on V8 and libevent. Unless some poor sod actually reimplements the entire nodejs stack... but I hope people are smarter than that. :-)

nknighthb3• 11 years ago

And what if those companies wish to provide their software to customers?

They can abide by the free license, or pay for a different license. Or, yes, switch to a different library. They are not entitled to use this library, nor any other library.

No, the GPL, especially the AGPL is inherently bad for libraries.

If this library were not available under any sort of open-source license, would you be making the same post, insisting it's "bad" for them not to give you free stuff?

nothrabannosir2• 11 years ago

Guys, it's double licensed. You are describing exactly the point: they don't want companies to use this without paying. Pay, and you can redistribute it to your clients.

This is basically for-profit code from a for-profit company, with a side dish of "open source for open source projects." It's like... like Github. Like Travis-CI. Like QT.

rossy• 11 years ago

The AGPL is a pain though. MuJS was going to be used to add JS scripting to mpv, but the patch has been put on hold since the devs realised it was AGPL licensed and it could cause license compatibility issues with compiled binaries or libmpv users. I don't think MuJS will be used by anyone outside of GhostScript until they change their license to a more reasonable one.

have_humility• 11 years ago

It's already used with MuPDF, and things that embed it. I was eyeballing it last week in the source tree for the EBookDroid fork "Document Viewer".

maemre• 11 years ago

Routers already use GPL'd software (Linux for example). However, I don't know effects of using AGPL over GPL in this case. I can see that without a linking exemption saying that _linked_ JS code is not subject to license terms, it wouldn't allow using proprietary JS code. But, what are the consequences of choosing AGPL over GPL?

An irrelevant anecdotal note: Router firms can make distribution of source code harder to circumvent GPL. A router firm that a friend works distributes source code using CDs. So if you bought a router and wanting the source code for modified kernel etc., you send your request using email/telephone/mail/fax and get your own copy via snail mail.

copx• 11 years ago

I see hate for the licensing model they chose. But think of it this way: who is their target audience?

People willing to pay for a commercial license.

Many companies which want to sell software release a GPL-ed version as a kind of demo (and being able to add the "open source" buzz word to the description of their product does not hurt either).

That the (A)GPL makes this library unusable for most people is the reason why they chose that license; not because of Free Software idealism but because of commercial interests.

robmccoll2• 11 years ago

If you are considering using this, please consider using Lua instead. Lua has decent performance on its own, great performance for a scripting language when using LuaJIT, plays well with others, is insanely embeddable, and is much easier to learn and work with. No language is perfect, but Javascript is a bit mediocre.

Aldo_MX2• 11 years ago

You are making assumptions about the needs of a project to endorse your favorite language.

Remember that languages are tools, not sport teams.

There are needs that completely disregard any of the benefits you mentioned with lua, for example:

  a) How can Lua help me run existing JavaScript code?

  b) Why is Lua more cost-effective than embeddable JavaScript interpreters considering the
     following:
     1. the cost of learning how to embed and work with the Lua interpreter
     2. the cost of learning the scripting language with all its implications: a different
        syntax, a different way to work enforced by its standard library (ex. 1-indexed
        arrays), new quirks (ex. commenting nested arrays), etc.
     3. the cost of training people from other areas which are already accustomed to
        JavaScript

justincormack• 11 years ago

(a) Tessel produced a pretty complete open source JS to Lua converter, which runs node[1]

(b) People are not dumb, they can learn Lua. It is easier than learning JavaScript.

[1] https://github.com/tessel/colony-compiler

amelius• 11 years ago

Also, how can we run Lua in the browser? And how does it compare to "native" javascript in terms of performance?

xavel10• 11 years ago

Maybe it's just me, but I'm not a particular fan of Lua-inspired pseudo-stackbased APIs.

I'm not sure why so many language devs insist on this terrible design. I fail to see anything good about it; It doesn't make the code smaller, it doesn't make the code faster, but it does make abstraction a royal pain in the buttocks.

Also, they couldn't have possibly chosen a worse license for a library that is going to most likely embedded statically in a program. Of all licenses, why AGPL? If it has to be GPL (whyever is none of my concern), why not LGPL?

anjbe• 11 years ago

The intent is clearly to promote sales of commercial licenses. Similar to why Oracle relicensed Berkeley DB from BSD to AGPL: “As of July 2011, Oracle's list price for non-copyleft Berkeley DB licenses varies between 900 and 13,800 USD per processor.” https://en.wikipedia.org/wiki/Berkeley_DB#Licensing

xavel10• 11 years ago

Well, that's just Oracle being Oracle. They did the same nonsense with Opensolaris, if I recall correctly.

chubot2• 11 years ago

What would you do instead of the stack-based API? That's the best design there is AFAIK.

Lua started out with something like Python's API (Lua 3.0 I think), but they changed it to use the explicit context and stack.

xavel10• 11 years ago

The grand majority of programming language APIs do not use a stack-based API. Really, stack-based APIs are an exception in just about every way, but not in a good way.

If your question is about cheap memory storage, linked list algorithms already exist, so there's really no good reason to use a faux stack to store data.

jaen• 11 years ago

Explicit stack-based interfaces are used for good reason: This allows simple accurate garbage collection (see eg. the Ruby API which requires somewhat error-prone conservative GC, Python which requires refcounts all over the place, or OCaml which requires annotating all local variables in a special block). A custom frame stack is also needed to have coroutines in pure ANSI C (two of the reasons Lua is popular).

sesquipedalian2• 11 years ago

I don't believe non-stack based APIs prevent the implementation of the features you just mentioned. You don't necessarily have to expose the underlying stack manipulation routines as your defacto API although it is easier to do so. My gripe with this technique is that it makes it much harder for the compiler to catch errors. Personally, I think it would be better to expose the API as helper functions that compose (and hide) the underlying stack routines.

sesquipedalian2• 11 years ago

Agreed. The biggest drawback IMHO is you defer errors that could have been caught at compile time to runtime if you had a saner interface.

vorbote• 11 years ago

Coming from the Artifex people, I suspect MuJS will be used by MuPDF to implement PDF embedded JavaScript forms.

Julio-Guerra• 11 years ago

I just embedded it on a PowerPC P2020DS processor as a baremetal program (using the newlib and by stubbing the syscalls) and it works, I get a baremetal javascript interpreter ;)

dmytrish• 11 years ago

Pretty good implementation:

    > [] == []
    false
    > [] + []

    > {} + []
    0
    > [] + {}
    [object Object]
    > {} + {}
    NaN

Although it fails in this part (should be [10, NaN, 2]):

    > [10, 10, 10].map(parseInt)
    10,0,2

MuJS: an embeddable JavaScript interpreter

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