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Author image Mahmoud A. Mehyar


JavaScript::Shell - Run Spidermonkey shell from Perl


    use JavaScript::Shell;
    use strict;
    use warnings;
    my $js = JavaScript::Shell->new();
    ##create context
    my $ctx = $js->createContext();
    $ctx->Set('str' => 'Hello');
    $ctx->Set('getName' => sub {
        my $context = shift;
        my $args    = shift;
        my $firstname = $args->[0];
        my $lastname  = $args->[1];
        return $firstname . ' ' . $lastname;
        function message (){
            var name = getName.apply(this,arguments);
            var welcome_message = str;
            return welcome_message + ' ' + name;
    my $val = $ctx->get('message' => 'Mamod', 'Mehyar')->value;
    print $val . "\n"; ## prints 'Hello Mamod Mehyar'


JavaScript::Shell will turn Spidermonkey shell to an interactive environment by connecting it to perl

With JavaScript::Shell you can bind functions from perl and call them from javascript or create functions in javascript then call them from perl


While I was working on a project where I needed to connect perl with javascript I had a lot of problems with existing javascript modules, they were eaither hard to compile or out of date, so I thought of this approach as an alternative.

Even though this sounds crazy to do, to my surprise it worked as expected - at least in my usgae cases


JavaScript::Shell connect spidermonkey with perl through IPC bridge using IPC::Open2 so execution speed will never be as fast as using C/C++ bindings ported to perl directly

There is another over head when translating data types to/from perl, since it converts perl data to JSON & javascript JSON to perl data back again.

Saying that, the over all speed is acceptable and you can take some steps to improve speed like

Data Transfer

Try to transfer small data chunks between processes when possible, sending large data will be very slow

Buffer Data

As of version 0.02 JavaScript::shell has a new method for dealing with large strings passed to/from javascript, use this feature when ever you want to send large data "strings" -- see buffer

Minimize calls

Minimize number of calls to both ends, let each part do it's processing. for eaxmple:

    ##instead of
        function East (){}
        function West (){}
        function North (){}
        function South (){}
    ##do this
        function all () {
        function East (){}
        function west (){}
        function North (){}
        function South (){}


Once you intiate JavaScript::Shell you can create as many contexts as you want, each context will has it's own scope and will not overlap with other created contexts.

    my $js = JavaScript::Shell->new();
    my $ctx = $js->createContext();

You can pass a hash ref with simple data to createContext method as a sandbox object and will be copied to the context immediately

    my $ctx->createContext({
        Foo => 'Bar',
        Foo2 => 'Bar2'



Initiates SpiderMonkey Shell


creates a new context


This will run javascript code in a blocking loop until you call jshell.endLoop() from your javascript code

    $js->Set('Name' => 'XXX');
        for (var i = 0; i < 100; i++){
    ##will never reach this point unless we call
    ## jshell.endLoop(); in javascript code as above


Sets/Defines javascript variables, objects and functions from perl

    ## set variable 'str' with Hello vales
    $ctx->Set('str' => 'Hello');
    ## set 'arr' Array Object [1,2,3,4]
    $ctx->Set('arr' => [1,2,3,4]);
    ## set Associated Array Object
    $ctx->Set('obj' => {
        str1 => 'something',
        str2 => 'something ..'
    ## set 'test' function
    ## caller will pass 2 arguments
    ## 1- context object
    ## 2- array ref of all passed arguments
    $ctx->Set('test' => sub {
        my $context = shift;
        my $args = shift;
        return $args->[0] . ' ' . $args->[1];
    ## javascript object creation style
    $ctx->Set('obj' => {});
    $ctx->Set('obj.name' => 'XXX');
    $ctx->Set('obj.get' => sub { });


get values from javascript code, returns a JavaScript::Shell::Value Object

    my $ret = $ctx->get('str');
    print $ret->value; ## Hello
    ## remember to call value to get the returned string/object

get method will search your context for a matched variable/object/function and return it's value, if the name was detected for a function it will run this function first and then returns it's return value

    $ctx->get('obj.name')->value; ## XXX
    ##you can pass variables when trying to get a function
    $ctx->get('test' => 'Hi','Bye')->value; ## Hi Bye
    ##get an evaled script values
    $ctx->get('eval' => qq!
        var n = 2;
        var x = 3;
    !)->value;  #--> 5


Calling javascript functions from perl, same as get but doesn't return any value



eval javascript code

        //javascript code
        var n = 10;
        for(var i = 0; i<100; i++){
            n += 10;


This function should be used only when dealing with passing large strings

    $js->Set('largeStr' => sub{
        my $js = shift;
        my $args = shift;
        ##we have a very large string we need to pass to
        return $js->buffer('large string');
    var str = largeStr();

The same thing can be done when sending large strings from javascript to perl

    var str = 'very large string we need to pass to perl';
    ##to consume this string from perl just get it
    my $str = $js->getBuffer();    


set error handler method, this method accepts a code ref only. When an error raised from javascript this code ref will be called with 2 arguments

  • JavaScript::Shell instance

  • error object - Hash ref

Error Hash has the folloing keys

  • message error message

  • type javascript error type: Error, TypeError, ReferenceError ..

  • file file name wich raised this error

  • line line number

  • stack string of the full stack trace

Setting error hnadler example

    my $js = JavaScript::Shell->new();
        my $self = shift;
        my $error = shift;
        print STDERR $error->{message} . ' at ' . $error->{line}


Destroy javascript shell / clear context

    my $js = JavaScript::Shell->new();
    my $ctx->createContext();
    ##clear context;
    ##close spidermonkey shell


This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.16.2 or, at your option, any later version of Perl 5 you may have available.


Copyright (C) 2013 by Mamod A. Mehyar <mamod.mehyar@gmail.com>