Isolate execution of JavaScript

Question

One of the limitation of JS that bugs me the most is the poor ability to isolate code's execution. I want to be able to control the context in which the code is executed, Something that achieve a similar effect to what `Script.createContext` & `Script.runInContext` in node.js does (node is using binding to the V8 engine, so i can't emulate their implementation). Here is the some reason why I want to isolate code execution: - Isolate the code from the global namespace (the `window` object and the also the `DOM`) , but I however need to be able reference function call on objects exposed in the context which must be executed synchronous which makes it almost impossible using a `WebWorker` for isolation. - By isolate the execution of code it would possible also be able to deallocate its definitions when no longer needed (memory management). I know one may achieve partly isolated execution by loading script into a `iframe`, this approach is however very heavy and uses a lot memory for a se…

Accepted Answer

You can isolate your code from the global namespace with a simple self executing function object:

```
(function() {
   // all your code goes here
   // nobody outside of your code can reach your top level variables here
   // your top level variables are not on the window object

// this is a protected, but top level variable
   var x = 3;

// if you want anything to be global, you can assign it to the window object.
   window.myGlobal = {};

function myTopLevelFunction(x,y,z) {
       // code here
   }

})();
```

If you want to have multiple ones of these execution contexts and be able to share between them, then you will have to rendezvous via one publicly known location, either a truly global variable or a property on a known DOM object or something like that. It is relatively common to declare one global namespace object and use properties off that for any access to things you're sharing among modules. I know it isn't completely perfect, but it works. Here's an example of the rendevous using a single global namespace object:

```
// module AAA
(function() {
   // module AAA code goes here

// set up global namespace object and whatever references we want to be global
   window.myModuleTop = window.myModuleTop || {};
   myModuleTop.AAA = {};
   myModuleTop.AAA.myFuncA = function() {};

})();

// module BBB
(function() {
   // module BBB code goes here

// set up global namespace object and whatever references we want to be global
   window.myModuleTop = window.myModuleTop || {};
   myModuleTop.BBB = {};
   myModuleTop.BBB.myFuncB = function() {};

})();
```

Isolate execution of JavaScript

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