ECMAScript closures all environment frames

closure-with-eval.js

/**
 * ECMAScript closures all environment frames
 * (by the spec), so closured "x" variable is
 * available in the dynamic `eval`.
 *
 * This example is made to show the difference
 * of the Python's closures implementation,
 * see it here: https://gist.github.com/734482
 *
 * by Dmitry A. Soshnikov
 */

function foo(x) {
  function bar(y) {
    console.log(eval(k));
  }
  return bar;
}

// create "bar"
var bar = foo(10);

var k = "y";

// execute bar
bar(20); // OK, 20 - "y"

k = "x";

bar(20); // OK, 10 - "x"