Access variable from code run in "eval" in Javascript

In 2015, creating a Function object is your best bet here, rather than using eval:

new Function('arg1', 'arg2', 'return arg1 + arg2')(3,4) // returns 7

You might have better luck using a Javascript parser, like the one used by JSHint/JSLint

here's a demo on safely using eval using "use strict"

window.onload = function(){
    'use strict'; 
    //use strict forces to run code in "strict mode" 
    //use strict prevents eval from 
    //contaminating the immediate scope

    //let's test with "foo"
    var foo = 'lol';

    //now code has "foo" but using "use strict" 
    //makes code in eval stay in eval
    //note that at the last of the code, foo is "returned"
    var code = 'var foo = {name: "Spock",greeting: function() {return "Hello " + foo.name;}}; foo';

    //store eval'ed code in evalO
    var evalstore = eval(code);

    console.log(evalstore); //code in eval stays in here, which is "inner foo"
    console.log(foo);       //"outer foo" is unharmed and daisy fresh
}​;

so whatever code you have, contain it in a function which will serve as your namespace. then have that function returned to the outside world stored as a variable. this demo shows how it can be constructed, however, works only if code is in object literal notation.

window.onload = function() {
    'use strict';

    var ns = 'lol';

    //code must be an object literal
    var code = '{name: "Spock",greeting: function(){return "Hello " + foo.name;}}';

    //store in a constructor to be returned
    var constructorString = 'var ns = function(){return ' + code + '}; ns'; 

    var evalNs = eval(constructorString);     //type function/constructor
    var evalObj = new evalNs()                //object instance

    console.log(evalNs);  //constructor
    console.log(evalObj); //the namespaced object
    console.log(ns);      //outer "ns" preserved
};​

​

Probably not what exactly OP was looking for but another option is to use outside variables to store values generated inside eval, as in:

var value;
var code = 'var foo = 42';
code = code.replace('var foo', 'value');
eval(code);
value // returns 42;