Run your String.js

/*
Description:
1) Function should accept two arguments:

arg: any type

object with properties:

param: string type.
func: string type. This string is a body of executable function
2) Function should evaluate code of string passed as 'func' with parameter arg passed as argument and return result of execution

Example:

var arg = 4,                         // arg for "string" function call
    obj = {
      param: 'num',                  // parameter name for function in string  
      func: 'return Math.sqrt(num)'  // function that need call with arg var
    };

runYourString(arg, obj)              // we expect it should return 2 which is a result of square root of 4
ps: Solution of this Kata just fun language trick.

Usage of this code in production is not recommended.
*/
function runYourString (arg, obj) {
   return new Function(obj.param, obj.func)(arg);
}