ExecJS 可以让你在 Ruby 中运行 JavaScript 代码。它会自动选择最佳的运行环境并执行你的 JavaScript 程序，并将结果赋值给 Ruby 对象。
ExecJS 支持如下平台
therubyracer - Google V8 embedded within Ruby
therubyrhino - Mozilla Rhino embedded within JRuby
Node.js
Apple JavaScriptCore - Included with Mac OS X
Microsoft Windows Script Host (JScript)
示例代码：
require "execjs" require "open-uri" source = open("http://coffeescript.org/extras/coffee-script.js").read context = ExecJS.compile(source) context.call("CoffeeScript.compile", "square = (x) -> x * x", bare: true) # => "var square;\nsquare = function(x) {\n return x * x;\n};"
