Convert javascript dot notation object to nested object

toNotationObject.js

const obj = {
  "start.headline": "1 headline",
  "start.subHeadline": "subHeadline",
  "start.accordion.headline": "2 headline",
  "start.accordion.sections.0.content": "content 0",
  "start.accordion.sections.0.iconName": "icon 0",
  "start.accordion.sections.1.headline": "headline 1",
  "start.accordion.sections.1.content": "content 1",
  "start.accordion.sections.1.iconName": "icon 1",
  "start.accordion.sections.2.headline": "headline 2",
  "start.accordion.sections.2.content": "content 2",
  "start.accordion.sections.2.iconName": "icon 2",
  "end.field": "add headline",
  "end.button": "add button",
  "end.msgs.success": "success msg",
  "end.msgs.error": "error msg",
};

const res = Object.keys(obj).reduce((res, key) => {
  const path = key.split('.');
  const lastIndex = path.length - 1;
  path.reduce(
    (acc, k, i, a) => acc[k] = lastIndex === i ?
    obj[key] :
    acc[k] || (/\d/.test(a[i+1]) ? [] : {}),
    res
  );
  return res;
}, {});

console.log(res);