Object.defineProperty(Object.prototype, 'deepVal', {
  enumerable: false,
  configurable: false,
  writable: false,
  value: function (string){
    var props = string.split("."),
        val = {};
    for(var key in this){
      val[key] = this[key];
    }
    for(var i = 0,len = props.length;i<len;i++){
      val = val[props[i]];
    }
    return val;
  }
});

var a = {
  "b" : {
    "c" : "d"
  }
};
console.log(a.deepVal("b.c")); // d