Transform camelCase keys of an object into snake_case

snakify.js

function snakifyKeys(fields) {
  // because this function can receive map of ArrayNodes, we have to do this
  let jsonFields = JSON.parse(JSON.stringify(fields));
  
  for (let key in jsonFields) {
    if (jsonFields[key] instanceof Object) {
      // we need to go deeper!
      jsonFields[key] = snakifyKeys(jsonFields[key]);
    }

    let snakeKey = key.replace(/\.?([A-Z]+)/g, function(x, y) {return '_' + y.toLowerCase();}).replace(/^_/, '');
    jsonFields[snakeKey] = jsonFields[key];
    // remove the unwanted camelCase key
    if (snakeKey !== key) {
      delete jsonFields[key];
    }
  }
  return jsonFields;
}