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https://github.com/fgasper/p5-javascript-quickjs

CPAN’s JavaScript::QuickJS
https://github.com/fgasper/p5-javascript-quickjs

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CPAN’s JavaScript::QuickJS

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README 

        
# NAME



JavaScript::QuickJS - Run JavaScript via [QuickJS](https://bellard.org/quickjs) in Perl



# SYNOPSIS



Quick and dirty …



    my $val = JavaScript::QuickJS->new()->eval( q<

        let foo = "bar";

        [ "The", "last", "value", "is", "returned." ];

    > );



… or load ES6 modules:



    my $js = JavaScript::QuickJS->new()->helpers();



    $js->eval_module( q/

        import * as coolStuff from 'cool/stuff';



        for (const [key, value] of Object.entries(coolStuff)) {

            console.log(key, value);

        }

    / );



# DESCRIPTION



This library embeds Fabrice Bellard’s [QuickJS](https://bellard.org/quickjs)

engine into a Perl XS module. You can thus run JavaScript

([ES2020](https://tc39.github.io/ecma262/) specification) directly in your

Perl programs.



This distribution includes all needed C code; unlike with most XS modules

that interface with C libraries, you don’t need QuickJS pre-installed on

your system.



# METHODS



## $obj = _CLASS_->new( %CONFIG\_OPTS )



Instantiates _CLASS_. %CONFIG\_OPTS have the same effect as in

`configure()` below.



## $obj = _OBJ_->configure( %OPTS )



Tunes the QuickJS interpreter. Returns _OBJ_.



%OPTS are any of:



- `max_stack_size`

- `memory_limit`

- `gc_threshold`



For more information on these, see QuickJS itself.



## $obj = _OBJ_->set\_globals( NAME1 => VALUE1, .. )



Sets 1 or more globals in _OBJ_. See below for details on type conversions

from Perl to JavaScript.



Returns _OBJ_.



## $obj = _OBJ_->helpers()



Defines QuickJS’s “helpers”, e.g., `console.log`.



Returns _OBJ_.



## $obj = _OBJ_->std()



Enables QuickJS’s `std` module and creates a global of the same name

that’s usable from both script and module modes.



This resembles `qjs`’s `--std` flag except that it _only_ enables

`std`, not `os`.



Returns _OBJ_.



## $obj = _OBJ_->os()



Like `std()` but enables QuickJS’s `os` module instead of `std`.



## $VALUE = _OBJ_->eval( $JS\_CODE )



Like running `qjs -e '...'`. Returns $JS\_CODE’s last value;

see below for details on type conversions from JavaScript to Perl.



Untrapped exceptions in JavaScript will be rethrown as Perl exceptions.



$JS\_CODE is a _character_ string.



## $promise = _OBJ_->eval\_module( $JS\_CODE )



Runs $JS\_CODE as a module, which enables ES6 module syntax.

Note that no values can be returned directly in this mode of execution.



Returns a promise that resolves once the module is loaded.



## $obj = _OBJ_->await()



Blocks until all of _OBJ_’s pending work (if any) is complete.



For example, if you `eval()` some code that creates a promise, call

this to wait for that promise to complete.



Returns _OBJ_.



## $obj = _OBJ_->set\_module\_base( $PATH )



Sets a base path (a byte string) for ES6 module imports.



Returns _OBJ_.



## $obj = _OBJ_->unset\_module\_base()



Restores QuickJS’s default directory for ES6 module imports

(as of this writing, it’s the process’s current directory).



Returns _OBJ_.



# TYPE CONVERSION: JAVASCRIPT → PERL



This module converts returned values from JavaScript thus:



- JS string primitives become _character_ strings in Perl.

- JS number & boolean primitives become corresponding Perl values.

- JS null & undefined become Perl undef.

- JS objects …

    - Arrays become Perl array references.

    - “Plain” objects become Perl hash references.

    - Function, RegExp, and Date objects become Perl

    [JavaScript::QuickJS::Function](https://metacpan.org/pod/JavaScript%3A%3AQuickJS%3A%3AFunction), [JavaScript::QuickJS::RegExp](https://metacpan.org/pod/JavaScript%3A%3AQuickJS%3A%3ARegExp),

    and [JavaScript::QuickJS::Date](https://metacpan.org/pod/JavaScript%3A%3AQuickJS%3A%3ADate) objects, respectively.

    - Behaviour is **UNDEFINED** for other object types.



# TYPE CONVERSION: PERL → JAVASCRIPT



Generally speaking, it’s the inverse of JS → Perl:



- Perl strings, numbers, & booleans become corresponding JavaScript

primitives.



    **IMPORTANT:** Perl versions before 5.36 don’t reliably distinguish “numeric

    strings” from “numbers”. If your perl predates 5.36, typecast accordingly

    to prevent your Perl “number” from becoming a JavaScript string. (Even in

    5.36 and later it’s still a good idea.)



- Perl undef becomes JS null.

- Unblessed array & hash references become JavaScript arrays and

“plain” objects.

- [Types::Serialiser](https://metacpan.org/pod/Types%3A%3ASerialiser) booleans become JavaScript booleans.

- Perl code references become JavaScript functions.

- Perl [JavaScript::QuickJS::Function](https://metacpan.org/pod/JavaScript%3A%3AQuickJS%3A%3AFunction), [JavaScript::QuickJS::RegExp](https://metacpan.org/pod/JavaScript%3A%3AQuickJS%3A%3ARegExp),

and [JavaScript::QuickJS::Date](https://metacpan.org/pod/JavaScript%3A%3AQuickJS%3A%3ADate) objects become their original

JavaScript objects.

- Anything else triggers an exception.



# MEMORY HANDLING NOTES



If any instance of a class of this distribution is DESTROY()ed at Perl’s

global destruction, we assume that this is a memory leak, and a warning is

thrown. To prevent this, avoid circular references, and clean up all global

instances.



Callbacks make that tricky. When you give a JavaScript function to Perl,

that Perl object holds a reference to the QuickJS context. Only once that

object is `DESTROY()`ed do we release that QuickJS context reference.



Consider the following:



    my $return;



    $js->set_globals(  __return => sub { $return = shift; () } );



    $js->eval('__return( a => a )');



This sets $return to be a [JavaScript::QuickJS::Function](https://metacpan.org/pod/JavaScript%3A%3AQuickJS%3A%3AFunction) instance. That

object holds a reference to $js. $js also stores `__return()`,

which is a Perl code reference that closes around $return. Thus, we have

a reference cycle: $return refers to $js, and $js refers to $return. Those

two values will thus leak, and you’ll see a warning about it at Perl’s

global destruction time.



To break the reference cycle, just do:



    undef $return;



… once you’re done with that variable.



You _might_ have thought you could instead do:



    $js->set_globals( __return => undef )



… but that doesn’t work because $js holds a reference to all Perl code

references it **ever** receives. This is because QuickJS, unlike Perl,

doesn’t expose object destructors (`DESTROY()` in Perl), so there’s no

good way to release that reference to the code reference.



# CHARACTER ENCODING NOTES



QuickJS (like all JS engines) assumes its strings are text. Since Perl

can’t distinguish text from bytes, though, it’s possible to convert

Perl byte strings to JavaScript strings. It often yields a reasonable

result, but not always.



One place where this falls over, though, is ES6 modules. QuickJS, when

it loads an ES6 module, decodes that module’s string literals to characters.

Thus, if you pass in byte strings from Perl, QuickJS will treat your

Perl byte strings’ code points as character code points, and when you

combine those code points with those from your ES6 module you may

get mangled output.



Another place that may create trouble is if your argument to `eval()`

or `eval_module()` (above) contains JSON. Perl’s popular JSON encoders

output byte strings by default, but as noted above, `eval()` and

`eval_module()` need _character_ strings. So either configure your

JSON encoder to output characters, or decode JSON bytes to characters

before calling `eval()`/`eval_module()`.



For best results, _always_ interact with QuickJS via _character_

strings, and double-check that you’re doing it that way consistently.



# NUMERIC PRECISION



Note the following if you expect to deal with “large” numbers:



- JavaScript’s numeric-precision limits apply. (cf.

[Number.MAX\_SAFE\_INTEGER](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER).)

- Perl’s stringification of numbers may be _less_ precise than

JavaScript’s storage of those numbers, or even than Perl’s own storage.

For example, in Perl 5.34 `print 1000000000000001.0` prints `1e+15`.



    To counteract this loss of precision, add 0 to Perl’s numeric scalars

    (e.g., `print 0 + 1000000000000001.0`); this will encourage Perl to store

    numbers as integers when possible, which fixes this precision problem.



- Long-double and quad-math perls may lose precision when converting

numbers to/from JavaScript. To see if this affects your perl—which, if

you’re unsure, it probably doesn’t—run `perl -V`, and see if that perl’s

compile-time options mention long doubles or quad math.



# OS SUPPORT



QuickJS supports Linux, macOS, and Windows natively, so these work without

issue.



FreeBSD, OpenBSD, & Cygwin work after a few patches that we apply when

building this library. (Hopefully these will eventually merge into QuickJS.)



# LIBATOMIC



QuickJS uses C11 atomics. Most platforms implement that functionality in

hardware, but others (e.g., arm32) don’t. To fill that void, we need to link

to libatomic.



This library’s build logic detects whether libatomic is necessary and will

only link to it if needed. If, for some reason, you need manual control over

that linking, set `JS_QUICKJS_LINK_LIBATOMIC` in the environment to 1 or a

falsy value.



If you don’t know what any of that means, you can probably ignore it.



# SEE ALSO



Other JavaScript modules on CPAN include:



- [JavaScript::Duktape::XS](https://metacpan.org/pod/JavaScript%3A%3ADuktape%3A%3AXS) and [JavaScript::Duktape](https://metacpan.org/pod/JavaScript%3A%3ADuktape) make the

[Duktape](https://duktape.org) library available to Perl. They’re similar to

this library, but Duktape itself (as of this writing) lacks support for

several JavaScript constructs that QuickJS supports. (It’s also slower.)

- [JavaScript::V8](https://metacpan.org/pod/JavaScript%3A%3AV8) and [JavaScript::V8::XS](https://metacpan.org/pod/JavaScript%3A%3AV8%3A%3AXS) expose Google’s

[V8](https://v8.dev) library to Perl. Neither seems to support current

V8 versions.

- [JE](https://metacpan.org/pod/JE) is a pure-Perl (!) JavaScript engine.

- [JavaScript](https://metacpan.org/pod/JavaScript) and [JavaScript::Lite](https://metacpan.org/pod/JavaScript%3A%3ALite) expose Mozilla’s

[SpiderMonkey](https://spidermonkey.dev/) engine to Perl.



# LICENSE & COPYRIGHT



This library is copyright 2023 Gasper Software Consulting.



This library is licensed under the same terms as Perl itself.

See [perlartistic](https://metacpan.org/pod/perlartistic).



QuickJS is copyright Fabrice Bellard and Charlie Gordon. It is released

under the [MIT license](https://opensource.org/licenses/MIT).