set-in.js

export const setIn = (obj: Object, key: string, value: string): Object => {
  const levels = key.split('.');

  const innerMostKey = levels.pop();
  const innerMost = { [innerMostKey]: value };

  const m = levels.reverse().reduce(
    (acc, curr) => ({
      [curr]: acc,
    }),
    innerMost as Object
  );

  return Object.assign(obj, m);
};