Split array entries to form object in JavaScript

Suppose, we have an array of string literals like this −

const arr = [
   "fiat−palio",
   "fiat−stilo",
   "fiat−strada",
   "fiat−uno",
   "fiat−uno",
   "gm−corsa",
   "gm−celta",
   "ford−fiesta",
   "volkswagen−gol",
   "volkswagen−gol",
   "volkswagen−gol",
   "volkswagen−voyage"
]

We are required to write a JavaScript function that takes in one such array of strings. In the above array, all the entries have one thing in common (besides all being a string), they all have a string pair separated by a dash ('−').

Our function should prepare an object that contains keys as the part before the dash ('−) and their values as objects which contains the count of each string they were within the original array.

Therefore, for the above array, the output should look like this −

const output = {
   "fiat": {
      "palio": 1,
      "stilo": 1,
      "strada": 1,
      "uno": 2
   },
   "gm": {
      "corsa": 1,
      "celta": 1
   },
   "ford": {
      "fiesta": 1
   },
   "volkswagen": {
      "gol": 3,
      "voyage": 1
   }
};

Example

The code for this will be −

const arr = [
   "fiat−palio",
   "fiat−stilo",
   "fiat−strada",
   "fiat−uno",
   "fiat−uno",
   "gm−corsa",
   "gm−celta",
   "ford−fiesta",
   "volkswagen−gol",
   "volkswagen−gol",
   "volkswagen−gol",
   "volkswagen−voyage"
];
const convertToObject = (arr = []) => {
   let res = arr.reduce((acc, val) => {
      let pair = val.split('−');
      let mark = pair[0];
      let model = pair[1];
      if(!acc.hasOwnProperty(mark)) {
         acc[mark] = {};
         acc[mark][model] = 1;
      } else {
         if(acc[mark].hasOwnProperty(model)) {
            acc[mark][model] += 1;
         } else {
            acc[mark][model] = 1;
         }
      }
      return acc;
   }, {})
   return res;
}
console.log(convertToObject(arr));

Output

And the output in the console will be −

{
   fiat: { palio: 1, stilo: 1, strada: 1, uno: 2 },
   gm: { corsa: 1, celta: 1 },
   ford: { fiesta: 1 },
   volkswagen: { gol: 3, voyage: 1 }
}