JSFiddle - React, Tailwind, and code Playground

JavaScript

var myObj = {
    first: {
        second:{
            third:"test"
        }
    }
};

var key = "first.second.third";

function get(obj, key) {
  var keys = key.split(".");
  var tmp = obj;
  for (var x = 0; x < keys.length; x++){
     tmp = tmp[keys[x]];
  }
  return tmp;
}

console.log(get(myObj, key));