Add the feature to update json2.js regulary from the upstream.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "vendor/JSON-js"]
+	path = vendor/JSON-js
+	url = https://github.com/douglascrockford/JSON-js.git

Rakefile

@@ -1,5 +1,7 @@
 require "rake/testtask"
 require "bundler/gem_tasks"
+require 'fileutils'
+require 'shellwords'
 
 task :default => :test
 
@@ -65,3 +67,15 @@ task :test do
   raise "test failures" if failed.any?
   raise "all tests skipped" if !passed.any?
 end
+
+desc "Rebuild lib/execjs/support/json2.js"
+task :js do
+  src = File.join('vendor', 'JSON-js', 'json2.js')
+  dest = File.join('lib', 'execjs', 'support', 'json2.js')
+  FileUtils.cp(src, dest)
+  patches = `#{['git', 'ls-files', 'patches', 'JSON-js'].shelljoin}`.split("\n")
+  patches.each do |patch|
+    `#{['patch', '-p1', '-i', patch].shelljoin}`
+  end
+  FileUtils.chmod(0644, dest)
+end

patches/JSON-js/0001-Ensure-JSON-var-isn-t-shadowed-in-JSC-and-Spidermonk.patch

@@ -0,0 +1,41 @@
+From f47c02c8536ce7cf0850b6a511fcecad6539eeaf Mon Sep 17 00:00:00 2001
+From: Joshua Peek <[email protected]>
+Date: Thu, 12 May 2011 10:24:07 -0500
+Subject: [PATCH] Ensure JSON var isn't shadowed in JSC and Spidermonkey
+
+---
+ lib/execjs/support/json2.js | 13 +++++++------
+ 1 file changed, 7 insertions(+), 6 deletions(-)
+
+diff --git a/lib/execjs/support/json2.js b/lib/execjs/support/json2.js
+index 36d3dc3..fb8fe0a 100644
+--- a/lib/execjs/support/json2.js
++++ b/lib/execjs/support/json2.js
+@@ -159,12 +159,13 @@
+ // Create a JSON object only if one does not already exist. We create the
+ // methods in a closure to avoid creating global variables.
+
+-var JSON;
+-if (!JSON) {
+-    JSON = {};
+-}
++(function (global) {
++    if (!global.JSON) {
++        global.JSON = {};
++    }
++
++    var JSON = global.JSON;
+
+-(function () {
+     "use strict";
+
+     function f(n) {
+@@ -477,4 +478,4 @@ if (!JSON) {
+             throw new SyntaxError('JSON.parse');
+         };
+     }
+-}());
++}(this));
+-- 
+2.5.5
+