do: magic({"a": {"b": {"c": "hey"}}}, "a.b.c") === "hey"

dirty.js

// Quick & Unsafe way...
// + with eval your var MUST be global & you MUST know its name

var obj = {"a": {"b": {"c": "hey"}}};
var path = "a.b.c";
console.log(magic(obj, path)); // hey
console.log(eval("obj."+path)); // hey
console.log(obj.a.b.c); // hey

var wrongPath = "b.c";
console.log(magic(obj, wrongPath)); // undefined
console.log(eval("obj."+wrongPath)); // Error
console.log(obj.b.c); // Error

magic.js

function magic(obj, path){
  if(path === ''){
    return obj;
  } else if(Array.isArray(path)){
    if(path.length > 0 && obj !== undefined){
      var attr = path.shift();
      return magic(obj[attr], path);
    } else {
      return obj;
    }
  } else {
    return magic(obj, path.split('.'));
  }
}

Object.prototype.getByPath = function(path){
  return magic(this, path);
};

console.log('magic', magic({"a": {"b": {"c": "hey"}}}, "a.b.c")); // hey
console.log('getByPath', {"a": {"b": {"c": "hey"}}}.getByPath("a.b.c")); // hey