How to parse INI file into nested associative array?

Question

I'm new to Javascript and I'm having trouble parsing an INI formatted file into nested objects.

The file I have is formatted like this:

ford.car.focus.transmission=standard
ford.car.focus.engine=four-cylinder
ford.car.focus.fuel=gas

ford.car.taurus.transmission=automatic
ford.car.taurus.engine=V-8
ford.car.taurus.fuel=diesel

purchased=Ford Taurus

I would like to have the structure look like this:

{ ford:
  { car:
    { focus:
      {
        transmission: 'standard',
        engine: 'four-cylinder',
        fuel: 'gas'
      }
    }
    { taurus:
      {
        transmission: 'automatic',
        engine: 'V-8',
        fuel: 'diesel'
      }
    }
  }
  purchased: 'Ford Taurus'
}

I'm storing the file in lines in an array, splitting on '\n'. I'm trying to write a method that would be called in a loop, passing my global object like this:

var hash = {};
var array = fileData.toString().split("\n");
for (i in array) {
  var tmp = array[i].split("=");
  createNestedObjects(tmp[0], tmp[1], hash);
}

This should let me access the values in the hash object like:

hash.ford.car.focus.fuel
# 'gas'

hash.purchase
# 'Ford Taurus'

I've tried something like what was suggested here: Javascript: how to dynamically create nested objects using object names given by an array, but it only seems to set the last item in the nest.

{ fuel: 'diesel',
  purchased: 'Ford Taurus' }

My unsuccessful attempt looks like this:

createNestedObjects(path, value, obj) {
  var keys = path.split('.');
  keys.reduce(function(o, k) {
    if (k == keys[keys.length-1]) {
      return o[k] = value;
    } else {
      return o[k] = {};
    }
  }, obj);
}

However, it will only return the last value for the nested values:

{ ford: { car: { taurus: { fuel: 'diesel' } } },
  purchased: 'Ford Taurus' }

createNestedObjects doesn't check whether the key already exists in the object, so it replaces it if it already exists. — Barmar
– Barmar, Commented Apr 9, 2016 at 0:25

vitaly-t · Accepted Answer · 2025-06-19 07:27:17Z

3

The function needs to check whether an intermediate key already exists before assigning to it.

function createNestedObjects(path, value, obj) {
    const keys = path.split('.');
    keys.reduce(function (o, k) {
        if (k == keys[keys.length - 1]) {
            return o[k] = value;
        }
        return o[k] ??= {};
    }, obj);
}

edited Jun 19 at 7:27

vitaly-t

26.1k18 gold badges129 silver badges151 bronze badges

answered Apr 9, 2016 at 0:26

Barmar

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