possible to use variable variables to reference the real object stored as a reference in JSON from a nodejs function

Is it possible to use variable variables in JS so that a JSON config file can be used to set the required object name and be accessed by a function?

take the following POST express code

//form passed to express has a field
req.body = {"myFieldA":"hello","myFieldB":"world"}

// store that as a reference in a JSON config file
config.js
{
   myFields:{
     alpha:"req.body.myFieldA",
     beta: "req.body.myFieldB"
   }
 }


//in server.js access the object by the JSON reference
import config from './config.js';
myVal = config.myFields.alpha;

// myval should now = "hello"