Reduce returns undefined

Question

I have an Array of Objects (Cars) :

var car = [
   {speed: 20, color: "red"},
   {speed: 5, color: "blue"},
   {speed: 80, color: "yellow"},
   {speed: 79, name: "orange"}
];

and a function that should return the fastest Car in the Array :

function getFastestCar(cars) {
   cars.reduce(function (prevFastestCar,curFastestcar) {
       if (curFastestcar.speed > prevFastestCar.speed) return curFastestcar;
       else return prevFastestCar;
   }, {speed: -Infinity, name: "test"});
};

After searching for a few hours I couldn´t find any solution why the function is returning undefined. I debugged the code and the function works perfectly fine, except in the last "step" it somehow replaces the fastest Car with undefined. I´m trying to understand the concept behind the reduce Method I know that there are easier ways to do this, but I´m curious why it is not working correctly.

Answer 1

This is probably just personal preference, but I don't like using Array.reduce for tasks involving comparison. I think the following is much easier to follow:

const cars = [
    {speed: 20, color: "red"},
    {speed: 5, color: "blue"},
    {speed: 80, color: "yellow"},
    {speed: 79, name: "orange"}
];

function getFastestCar(cars) {
    var fastestCar = {};
    if (cars.length) {
        cars.forEach(car => {
            fastestCar = fastestCar.speed > car.speed ? fastestCar : car;
        });
    }
    return fastestCar;
}

console.log(getFastestCar(cars));

Answer 2

You need to return the reduced value from the function.

return cars.reduce(..);

See the description of reduce.

Return value

The value that results from the reduction.