scope.js

var foo = function () { 
  var a = 3;
  var b = 5;
  var bar = function () { 
    var b = 7;
    var c = 11; // a === 3, b === 7, c === 11
    a += b + c; // a === 21, b === 7, c === 11
  };
  // a === 3, b === 5, c === undefined
  bar();
  // a === 21, b === 5, c === undefined
};