How To Force Reduce To NOT Sorting Alphabetically In JavaScript

I need to group by my elements in array so I did in that way: const cars = [{ make: 'vw', model: 'passat', year: '2012' }, { make: 'vw',

Solution 1:

reduceRight applies the reduce from right to left. Just don't use the Right variant and it'll be in the original order.

const cars = [{
        make: "vw",
        model: "passat",
        year: "2012"
    },
    {
        make: "vw",
        model: "golf",
        year: "2013"
    },
    {
        make: "ford",
        model: "mustang",
        year: "2012"
    },
    {
        make: "ford",
        model: "fusion",
        year: "2015"
    },
    {
        make: "kia",
        model: "optima",
        year: "2012"
    }
];

let group = cars.reduce((r, a) => {
  r[a.make] = [...r[a.make] || [], a];
  return r;
 }, {});

console.log(cars)
console.log(group)

There was a bug in your original code, you were assigning properties of an array. There's no point to this; use an object instead.