Reducing an array into an object in Javascript

I want to turn the following object

const order = {
  apple: 5,
  banana: 5,
  orange: 5
};

into the following object, with each key being assigned its index in the object as its value

{
  apple: 0,
  banana: 1,
  orange: 2
}

This is the code I have but it’s not working and I don’t know why.

const indices = Object.keys(order).reduce(
    (previousValue, currentValue, currentIndex) =>
      (previousValue[currentValue] = currentIndex), {}
  );
TypeError: Cannot create property 'banana' on number '0'

What am I doing wrong here?

>Solution :

Reducer is expected to return the accumulator:

const order = {
  apple: 5,
  banana: 5,
  orange: 5
};

const indices = Object.keys(order).reduce(
  (previousValue, currentValue, currentIndex) => {
    previousValue[currentValue] = currentIndex;
    return previousValue; // <-- this was missing in your attempt.
  }, {}
);

console.log(indices);