How to flatten a JavaScript object into a daisy chain like form?

Question

I want to flatten an object like this...

var obj1 = {
  firstName: 'John',
  lastName: 'Green',
  car: {
    make: 'Honda',
    model: 'Civic',
    revisions: [
      { miles: 10150, code: 'REV01', changes: },
      { miles: 20021, code: 'REV02', changes: [
        { type: 'asthetic', desc: 'Left tire cap' },
        { type: 'mechanic', desc: 'Engine pressure regulator' }
      ] }
    ]
  },
  visits: [
    { date: '2015-01-01', dealer: 'DEAL-001' },
    { date: '2015-03-01', dealer: 'DEAL-002' }
  ]
};

... into a daisy chain form like the following:

{
    "firstName": "John",
    "lastName": "Green",
    "car.make": "Honda",
    "car.model": "Civic",
    "car.revisions.0.miles": 10150,
    "car.revisions.0.code": "REV01",
    "car.revisions.0.changes": ,
    "car.revisions.1.miles": 20021,
    "car.revisions.1.code": "REV02",
    "car.revisions.1.changes.0.type": "asthetic",
    "car.revisions.1.changes.0.desc": "Left tire cap",
    "car.revisions.1.changes.1.type": "mechanic",
    "car.revisions.1.changes.1.desc": "Engine pressure regulator",
    "visits.0.date": "2015-01-01",
    "visits.0.dealer": "DEAL-001",
    "visits.1.date": "2015-03-01",
    "visits.1.dealer": "DEAL-002"
}

Here's my (failed) attempt:

function flatten(obj) {
    var flattenObject = {};

    // iterate given object
    for (let x in obj) {
        if (typeof obj[x] == 'string') {
            flattenObject[x] = obj[x];
        }

        if (typeof obj[x] == 'object') {
            for (let y in obj[x]) {
                flattenObject[x + '.' + y] = obj[x][y];
            }
        }
    }

    return flattenObject;
}

I quickly started repeating code unnecessarily in order to daisy chain inner objects and arrays. This is definitely something that needs recursion. Any ideas?

EDIT: This question is similar to other questions but not a duplicate. This question requires a specific notation and nested objects and arrays at the same time.

EDIT: I've also asked the opposite, unflatten, in another question.

Answer 1

Here's my code (typesciprt)

export const flatten = (data: object, prefix: string = '') => {
  const result: { [key: string]: string | number | null } = {};

  Object.entries(data).forEach(([key, value]) => {
    if (typeof value === 'object') {
      Object.assign(result, flatten(value, `${prefix}${key}.`));
    } else {
      result[`${prefix}${key}`] = value;
    }
  });

  return result;
};

javascript version

export const flatten = (data, prefix = '') => {
  const result = {};

  Object.entries(data).forEach(([key, value]) => {
    if (typeof value === 'object') {
      Object.assign(result, flatten(value, `${prefix}${key}.`));
    } else {
      result[`${prefix}${key}`] = value;
    }
  });

  return result;
};