therubyrhino

Embed the Mozilla Rhino JavaScript interpreter into Ruby

• JRuby >= 1.6.8

jruby -S gem install therubyrhino

• Evaluate JavaScript from with in Ruby
• Embed your Ruby objects into the JavaScript world

1. JavaScript goes into Ruby
2. Ruby Objects goes into JavaScript
3. Our shark's in the JavaScript!

require 'rhino'

• evaluate some simple JavaScript using eval_js:

eval_js "7 * 6" #=> 42

• that's quick and dirty, but if you want more control over your environment, use a Context:

Rhino::Context.open do |context|
  context['foo'] = "bar"
  context.eval('foo') # => "bar"
end

• evaluate a Ruby function from JavaScript:

Rhino::Context.open do |context|
  context["say"] = lambda {|word, times| word * times}
  context.eval("say('Hello', 3)") #=> HelloHelloHello
end

• embed a Ruby object into your JavaScript environment

class MyMath
  def plus(a, b)
    a + b
  end
end

Rhino::Context.open do |context|
  context["math"] = MyMath.new
  context.eval("math.plus(20, 22)") #=> 42
end

• make a Ruby object be your JavaScript environment

math = MyMath.new
Rhino::Context.open(:with => math) do |context|
  context.eval("plus(20, 22)") #=> 42
end

# or the equivalent

math.eval_js("plus(20, 22)")

• make your standard objects (Object, String, etc...) immutable:

Rhino::Context.open(:sealed => true) do |context|
  context.eval("Object.prototype.toString = function() {}") # this is an error!
end

• turn on Java integration from JavaScript (probably a bad idea):

Rhino::Context.open(:java => true) do |context|
  context.eval("java.lang.System.exit()") # it's dangerous!
end

• limit the number of instructions that can be executed to prevent rogue code:

Rhino::Context.open(:restrictable => true) do |context|
  context.instruction_limit = 100000
  context.eval("while (true);") # => Rhino::RunawayScriptError
end

• limit the time a script executes (rogue scripts):

Rhino::Context.open(:restrictable => true, :java => true) do |context|
  context.timeout_limit = 1.5 # seconds
  context.eval %Q{
    for (var i = 0; i < 100; i++) {
      java.lang.Thread.sleep(100);
    }
  } # => Rhino::ScriptTimeoutError
end

In addition to just evaluating strings, you can also use streams such as files:

• evaluate bytes read from any File/IO object:

  File.open("mysource.js") do |file|
    eval_js file, "mysource.js"
  end

• or load it by filename:

  Rhino::Context.open do |context|
    context.load("mysource.js")
  end

By default accessing Ruby objects from JavaScript is compatible with therubyracer: https://github.com/cowboyd/therubyracer/wiki/Accessing-Ruby-Objects-From-JavaScript

Thus you end-up calling arbitrary no-arg methods as if they were JavaScript properties, since instance accessors (properties) and methods (functions) are indistinguishable:

Rhino::Context.open do |context|
  context['Time'] = Time
  context.eval('Time.now')
end

However, you can customize this behavior and there's another access implementation that attempts to mirror only attributes as properties as close as possible:

class Foo
  attr_accessor :bar

  def initialize
    @bar = "bar"
  end

  def check_bar
    bar == "bar"
  end
end

Rhino::Ruby::Scriptable.access = :attribute
Rhino::Context.open do |context|
  context['Foo'] = Foo
  context.eval('var foo = new Foo()')
  context.eval('foo.bar') # get property using reader
  context.eval('foo.bar = null') # set property using writer
  context.eval('foo.check_bar()') # called like a function
end

If you happen to come up with your own access strategy, just set it directly :

Rhino::Ruby::Scriptable.access = FooApp::BarAccess.instance

The Ruby Rhino is designed to let you evaluate JavaScript as safely as possible unless you tell it to do something more dangerous. The default context is a hermetically sealed JavaScript environment with only the standard objects and functions. Nothing from the Ruby world is accessible.

For Ruby objects that you explicitly embed into JavaScript, only the +public+ methods "defined in their classes" are exposed by default e.g.

class A
  def a; 'a'; end
end

class B < A
  def b; 'b'; end
end

Rhino::Context.open do |context|
  context['a'] = A.new
  context['b'] = B.new
  context.eval("a.a()") # => 'a'
  context.eval("b.b()") # => 'b'
  context.eval("b.a()") # => 'TypeError: undefined property 'a' is not a function'
end

Just like the JVM packaged Rhino scripting engine, therubyrhino gem supports specifying JavaScript context properies (optimization level and language version) using system properties e.g. to force interpreted mode :

jruby -J-Drhino.opt.level=-1 -rtherubyrhino -S ...

You might also set these programatically as a default for all created contexts :

Rhino::Context.default_optimization_level = 1
Rhino::Context.default_javascript_version = 1.6

Or using plain old JAVA_OPTS e.g. when setting JavaScript version :

-Drhino.js.version=1.7

Rhino is currently maintained at https://github.com/mozilla/rhino Release downloads are available at http://www.mozilla.org/rhino/download.html Rhino is licensed under the MPL 1.1/GPL 2.0 license.

Officially supported versions of Rhino's js.jar are packaged separately as therubyrhino_jar gem. Make sure you're using the latest gem version if you feel like missing something available with Rhino. For experimenters the jar can be overriden by defining a Rhino::JAR_PATH before require 'rhino' e.g. :

module Rhino
  JAR_PATH = File.expand_path('lib/rhino/build/rhino1_7R5pre/js.jar')
end
# ...
require 'rhino'

(The MIT License)

Copyright (c) 2009-2015 Charles Lowell

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.