Using contextify to replace vm second version

vm.js

var vm = function(){
  //avoid contextify's js wrapper
  var contextifyPath = require('path').resolve(require.resolve('contextify'), '..', '..');
  var contextify = require('bindings')({
    module_root: contextifyPath,
    bindings: 'contextify.node'
  });
  // basic WeakMap shim if not available
  var WM = typeof WeakMap !== 'undefined' ? WeakMap : function WeakMap(){
    var keys = [], values = [];
    return {
      set: function(key, val){
        keys.push(key);
        values.push(val);
        return val;
      },
      get: function(key){
        var index = keys.indexOf(key);
        if (~index) return values[index];
      },
      has: function(key){
        return !!~keys.indexOf(key);
      },
      delete: function(key){
        var index = keys.indexOf(key);
        if (~index) {
          keys.splice(index, 1);
          values.splice(index, 1);
          return true;
        }
        return false;
      }
    };
  };


  // allow for proper garbage collection
  var contexts = new WM;
  var Context = contextify.ContextifyContext;


  function createContext(sandbox){
    if (sandbox == null) {
      sandbox = {};
    } else if (Object(sandbox) !== sandbox) {
      throw new TypeError('Sandbox must be an object');
    }
    contexts.set(sandbox, new Context(sandbox));
    return sandbox;
  }

  function runInContext(code, sandbox){
    if (Object(sandbox) === sandbox) {
      if (!contexts.has(sandbox)) {
        createContext(sandbox);
      }
      return contexts.get(sandbox).run(code);
    } else {
      throw new TypeError('Context must be an object');
    }
  }

  function runInThisContext(code){
    return runInContext(code, global);
  }

  function runInNewContext(code){
    var sandbox = createContext();
    var result = runInContext(code, sandbox);
    dispose(sandbox);
    return result;
  }

  function dispose(sandbox){
    contexts.delete(sandbox);
  }

  return {
    createContext: createContext,
    runInContext: runInContext,
    runInThisContext: runInThisContext,
    runInNewContext: runInNewContext,
    dispose: dispose
  };
}();


console.log('### setup');
var sandbox = { test: 5 };
var o = vm.createContext(sandbox);
console.log(o === sandbox); // true
console.log(o);
console.log(sandbox);



console.log('\n### no leaks');
console.log(vm.runInContext('typeof run', o)); // undefined
console.log(vm.runInContext('typeof getGlobal', o)); // undefined



console.log('\n### dynamic updates');

sandbox.thing = [555];
console.log(vm.runInContext('thing', o)); // [555]

vm.runInContext('thing2 = { a: 666 }', o);
console.log(sandbox.thing2); // { a: 666 }

o.thing3 = '777';
console.log(sandbox.thing3); // 777

sandbox.thing4 = 888;
console.log(o.thing4) // 888

o.thing5 = /999/;
console.log(vm.runInContext('thing5', o)) // /999/


console.log('\n### compare');

function getExternalGlobal () { return o }
function getLocalGlobal () { return vm.runInContext('this', o) }
o.getExternalGlobal = getExternalGlobal;
o.getLocalGlobal = getLocalGlobal;
o.externalGlobal = o;
o.localGlobal = vm.runInContext('this', o);


console.log(vm.runInContext("this === getExternalGlobal()", o)); // false
console.log(vm.runInContext("this === getLocalGlobal()", o)); // true
console.log(vm.runInContext("this === externalGlobal", o)); // false
console.log(vm.runInContext("this === localGlobal", o)); // true