local variable overriding

test.js

// Almak istedigimiz degisken 'a'
function Vehicle(){
}

Vehicle.prototype.go = function(){
  var a = "deneme"
}


// Fonksiyondaki kod calismadan yukle
function getVariable() {
  $buDegiskeneAl = null;
  goFunc = Vehicle.prototype.go;
  oldCode = goFunc.toString();
  oldCodePart1 = oldCode.slice(0,oldCode.length-1);
  oldCodePart2 = "}";
  codeToInsert = "$buDegiskeneAl = a";
  var newCode = oldCodePart1 + codeToInsert + oldCodePart2;
  var newFunc = eval("newCode")
  eval ("Vehicle.prototype.go= " + newFunc);
}
getVariable();

// 'a' nin bulundugu fonksiyon calissin
var v = new Vehicle();
v.go()


console.log($buDegiskeneAl)