Is it possible to restrict the scope of a javascript function?

Question

Suppose I have a variables in the global scope.

Suppose I wish to define a function which I can guarantee will not have access to this variable, is there a

Answer 1

You can use WebWorkers to isolate your code:

Create a completely separate and parallel execution environment (i.e. a separate thread or process or equivalent construct), and run the rest of these steps asynchronously in that context.

Here is a simple example:

someGlobal = 5;

//As a worker normally take another JavaScript file to execute we convert the function in an URL: http://stackoverflow.com/a/16799132/2576706
function getScriptPath(foo) {
  return window.URL.createObjectURL(new Blob([foo], {
    type: 'text/javascript'
  }));
}

function protectCode(code) {
  var worker = new Worker(getScriptPath(code));
}

protectCode('console.log(someGlobal)'); // prints 10
protectCode('console.log(this.someGlobal)');
protectCode('console.log(eval("someGlobal"))');
protectCode('console.log(window.someGlobal)');

This code will return:

Uncaught ReferenceError: someGlobal is not defined

undefined

Uncaught ReferenceError: someGlobal is not defined and

Uncaught ReferenceError: window is not defined

so you code is now safe.